Yeah, this set off alarm bells for me as well. That's far too much career risk for me, and I imagine for many others.
IMHO firing, especially early on, should be viewed as a failure of the recruiting process; it's expensive and time-consuming to hire an employee and then fire them compared to just saying no before an offer is made. I find it strange that the author seems to think that a high firing rate is something to be proud of.
This sounds like the worst employer I've ever heard of. A 50% chance of being fired? There's no way I'd take an offer if I knew that statistic.