Here's a great question (and answers) on the differences between Architectural Patterns and Design Patterns:
According to this (and filtered through my understanding), the component based way of Unity is closer to a design pattern than an architectural pattern.
I believe that because as you say (and I think so too) architectural patterns are more high level than design patterns (i.e. architectural patterns are about the whole system, as viewed from a high level, while design patterns refer to more granular components). As such the architectural level of Unity deals with the fact that you have a game loop, and how that game loop is designed and acts on everything you have in there (entities, physics, collisions, etc). The design level of unity deals with a lower level and more specific part, namely how each of the elements which are just listed in the architectural design is more actually...well.. designed, entities included.
So I guess we can talk about Unity's architecture as being one "specific to"/"good for" a game engine (game loop and the classification of the elements it interacts with in various categories like game objects, physics, collisions, etc), and then we can talk about the design pattern for each of these elements (a game object supports this and that component, it can have behaviors attached to it, etc. In turn the design pattern for the behaviors is "each is an object of a certain class in a certain OO language).