Not true from the anecdotes, and admittedly just anecdotes, that I've seen. Top performers get some token, Approved by Legal™, <2% cut to avoid it being classified as a low performer firing, with a larger but still proportional percent coming from middle performers, and the the vast majority of the layoff percent consisting of low performers.
Well, then I'll give you more anecdotes: I've been through, in one way or another, three layoffs in the last 7 years, and none of them were performance based.
Layoffs show the company isn't in a good place, so the best people start looking for better opportunities early, to avoid still being around when it gets even worse.