Yeah, sounds that way, if it's almost literally the same code rejiggered to build as C. A proper clean-room rewrite effort would be so much slower. You'd need one guy in IDA decompiling/understanding, then explaining the design of how it should work to read and render the assets etc without actually writing the code to do that, and someone different reading the spec and implementing it without touching the original code at all. Or a single person doing both halves but being almost impossibly strict about it.