It's bullshit because he doesn't know what it does, or seen identically prepared race engines with and without it...
If you can do it for free, go for it.
Cryo treating doesn't magically increase the strength of a part, but what it
does do is freeze a part so cold that the molecular composition of the metal shrinks, forcing tighter structure, and thus relieving any internal stress the part might have from slight density differences. As the part is allowed to warm back up, it returns back to it's original shape, but again, the internal stresses are relieved.
The benefit of this is having a part with no predisposition to breaking in a certain way under stress. With no predisposition, it's better able to cope with stress during engine operation, to a larger degree. The stress threshold of the part is the same as it was before cryo-treating, but there's no internal stress "adding to" that total, so you get a higher realized threshold.
Cryo treating is much like blueprinting, it's largely mis-understood by armchair engine builders, and dismissed as unnecessary, or "bullshit", but that's just fine for the rest of us that have seen more engines come apart in racing than most have even put together. Cryo-treating is starting to become like blueprinting in the engine building world, it's done so often that it's not even worth mentioning.