What do you mean by "developer level"?  Are you asking how difficult it would be to create?

Looks like a relatively simple game for an experienced developer, but no game will be 'easy' to make if you're just getting started, and the difficulty of a particular game will vary from one developer to another depending on their specific skill set, time available, etc.

Also, keep in mind that you're looking at a finished product. What you don't see is all of the scaffolding that went into getting to the finished product. All of that requires time and experimentation, but like the rough draft of a novel, nobody ever sees it. What may look like a 3 week project on the surface, could have taken 9 weeks to produce, etc.