By way of analogy
A circuit does not generate power. A light bulb does not generate power. A battery does not generate power. None of the things which use or store generated power, are power generators.
A gasoline-driven generator is a power generator.
A solar panel setup is a power generator. They can be expected to spontaneously generate when they are kicked off. Other things can use that power they generate: fridges and TVs and PCs and heaters and light bulbs.
Likewise, any code or program that actually generates content itself at runtime is PCG. The rest are just users of that procedurally-generated content (PGC). Now,
Procedural Content Generation
is not the same as
Procedurally-Generated Content
PGC is the resultant artifact of a process (program) which engages in PCG.
PCG is developed (programmed) to a point where it can autonomously produce content to some or other specification, but in (typically) countless variations; PGC is generated thereby as one single variation of the otherwise limitless possible content spaces within that broader algorithmic specification. PGC's are finite and static once generated. PCGs deal with infinity (or near enough).
Addressing specifics
"Procedural Content Generation" refers to code / applications which generate content.
Any game can be considered a PCG game if, at runtime it dynamically generates new content via part of its instruction set.
If you (or your engine) use(s) some other program code that generates content, then include that content as part of your game at compile / build time, then your game (and it's code) is NOT PCG. Hence:
a game engine capable of integrating automatically generated vegetation
...is not PCG, since that engine itself does not produce new content at runtime, it simply uses generated content from elsewhere, that has been manually included by artists, designer or devs.
recognizes the game map
PCG has nothing to do with recognition. It has to do with doing the active work of creating content. Generally PCG applications produce their own format of data that they can already understand and work with. They do not typically read in outside sources, although when they do, that is just plain old program logic... not PCG as such. PCG is all about generation. Hence PCG and not PCR :)
Historical perspectives
What we consider "content" in this context generally covers those things which, in the past, humans have had to produce by themselves. For example in the '70s and '80s, pretty much every game (with the exception of a very special few) had to have its art, its storyline, its music, its character and planet names, and suchlike, produced by a human being. That was the polar opposite of PCG.
PCG began when game programmers realised that instead of the rigmarole of hiring artists, musicians, writers etc. - and then still having to integrate their work with the code, or worse yet, doing all of that work themselves as well as coding - they could instead write programs to generate all that stuff for them. Those efforts were some of the first truly PCG functions, modules, and programs. A perfect example is the original XCom / UFO, where the game's code generates a completely unique level for you before combat. Earlier still (1979) was Temple of Apshai.
Elite was a different case: some of its content was generated when the game was under development; not only was that code written by the very same authors, but also that pre-generated content was typically used at runtime of elite.exe (i.e. when you the player ran the game) by further generators which were part of the game's code, creating the world you played in.
A newer example is Minecraft (and other games inspired by it) where the world literally generates around you as you walk toward the horizon, thanks in large part to modern computing power. Compare this to Rogue or Moria played on a PC-XT in the 1980s, for which you might have to sit sometime waiting for the level to generate! (depending on your chosen game settings).
Not all PCG is historically rooted in the games industry. For example, there are those who write fiction generators. For example, Ken Perlin in the field of graphics and computational geometry created the Perlin Noise algorithm, for which he was later given an academy award. For example, the musician Brian Eno has for a long time engaged in procedural generation of musical scores. And as another example, non-digital boardgames like HeroQuest/Warhammer Quest long ago invented procedural dynamics for creating a different gameboard on each play.
