I think he has said this in some stream and the majority of the time was spent on the game. He also said many times that the game is way more difficult to make than the compiler.
Rust was created on a Mozilla payroll to provide a C++ alternative with better concurrency support for the purpose of browser engine rewrite. Also, Rust doesn't have a 'creator', the person tasked with leading the project didn't have the authority to make the decisions, see https://graydon2.dreamwidth.org/307291.html
If I remember correctly, the game was just a showcase to test the new language.
Afaik that's exactly why it's a sokoban clone, because he didn't want to spend time inventing new mechanics.
Sorry, but no. Just because the graphics have some cartoony stylization does not mean that a lot of thought and effort did not go into them, not to mention lots of work from artists. You absolutely could not recreate something that looks like that with python in a few weeks. Not that the language/engine was strictly necessary to do so either, but you’re way off-base in terms of the level of work and effort required for these things.
Hopefully, jai and the engine will help make the next game faster...