Yes, you could. You could your product whatever you wanted, really. It's your product.
There isn't a strict definition for the term "game engine" within the industry. Most people will probably agree that an "engine" provides some reusable components and tools, typically at a high level, for building a product like a game and a "game engine" specifically provides those tools with the intent of building a complete game (versus a "physics engine" which only focuses on providing functionality to simulate physics).
Using other frameworks/APIs/engines underneath the abstraction of your own engine (or even exposing them) doesn't itself invalidate your use of the term "engine." It may not be the best idea, but that isn't what you asked.