The LAGA link is gold. Wish I could give more upvotes.

This paragraph I think gives context to both the HN thread author and the commenter:

Geometric algebra as practiced today originated in the 1960’s. It is currently under vigorous development. It has found important applications in computer science (in graphics, robotics, and computer vision), engineering, and physics. It is available to game developers for the Xbox and PlayStation video game consoles. This text is an attempt to keep up with these modern developments.

Putting on my must read/study list (I am proficient in linear algebra, so hoping for a gentle push into geometric algebra)