The actual algorithms used in that game are fairly trivial, and he didn't invent them or anything, nor was coding them up a huge challenge.
They are not that trivial. Writing a 2.5D renderer and understanding BSP trees is quite hard. Not the hardest thing on the planet, but requires a guy with decent amount of experience.
Ok, so let's walk this through then. This is what he wrote:
Problem with proprietary 'free' offerings
You never know when they will get killed. Same goes for Free Sharepoint, Free Office 365, Free One Drive etc. Get off them and breathe free.
Please tell me how that is related to open source.
You know what was a really good Microsoft offering, for its time? Microsoft Dinosaurs. And I liked Encarta as well.
Microsoft Dangerous Creatures for the life! Indeed, in general those multimedia CD-ROMs produced by Microsoft were very well executed.
If all else fails, lower your standards.