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That first one doesn't make any sense. Every processor has its own assembly language. The game would run on YOUR machine and any others running the same processors, but you'd have to build a custom version for any other processor you want to support.
That said, it could potentially be insanely well optimized for that platform if everything was hand coded.
That one is about Chris Sawyer. He'll remind people that there was a bit of C in there, but 99% x86 assembly / machine code in his words.
I think he only used C to build the installer. The rest was coded in x86 assembly.
Building anything in x86 assembly is a gargantuan effort, but then Chris Sawyer built a game on the same level of scale as RollerCoaster Tycoon...
There is some C in the game as well:
It's 99% written in x86 assembler/machine code (yes, really!), with a small amount of C code used to interface to MS Windows and DirectX.
https://web.archive.org/web/20201108105209/http://www.chrissawyergames.com/faq3.htm
For anyone interested in why, C was new and didn't yet optimize to the same level that a clever and experienced human could optimize Assembly. IIRC, by the time he was developing Roller Coaster Tycoon, C compiler optimization was on par with human Assembly optimization, so it was the last notable game written entirely in Assembly for optimization purposes.
I think this was the video I watched where I learned this: https://youtu.be/0JouTsMQsEA