They're not saying swapping equal valued variables breaks it. It's when the pointer is the same, using the trick to swap a variable with itself will set the variable to 0.
The trailer is intentionally vague to avoid spoilers. I thought the same thing playing through the game for the first hour or so until I got to a puzzle that made me realize why they built their own engine.
MINOR SPOILERS: Some of the later puzzle mechanics rely on playing with lighting and perspective in a way that seems to me would be difficult to implement in a stock engine.
In regards to them using a law firm in Texas, it may be due to favorable courts there for intellectual property holders. The first article I found about this talks specifically about patents [0], but I wouldn't be surprised if the courts were similarly favorable for other matters of intellectual property.
In a similar vein, the cantor function [1] (also known as the devil's staircase) is continuous and has derivative 0 almost everywhere, but still manages to increase in value.