Building an engine in construct 3?

I think they likely mean a framework, not an engine. But I guess in theory you could build an engine too, or at least something that resembles one.

An "engine" is simply the code behind your game. For example you can create a platform engine with movements, jumping etc, but its not a "game" until you have designed the levels, added the enemies etc.

I guess it depends on how you want to term it.

Games like Rust use Unity as the engine behind their game.

Games like Eve Online, which is created primarily in Python, the game is the engine.

To coders, it's semantics...

To the public though, it's public perceptions and thus, marketing. When the word engine appears, people think of that thing under the hood of their car that makes it go. To most, it's a mysterious, mechanical marvel that they can stare at in wonder and admire, but don't have to think too much about. Calling the code behind a game an 'engine' imparts that same mystery.

It's the same exact reason that the food industry wants to change 'high-fructose corn syrup' into 'corn sugar': public perceptions and thus, marketing.

Fair enough.