Certainly it contains a number of stories that I recognize and associate with that name, as well as a couple of semi-stand-alone chunks out of the "Argo/Devil Is Dead" novels. But I'm pretty sure it's not an official publication of the complete short stories of RAL.
There are over 200 stories in this file, and to even attempt to go through them one by one would be deepest insanity - even to categorizethem is pretty much hopeless. What they all have in common -- no: what they all are,, is Lafferty stories, and Lafferty was sui generis. Possibly even sui two or three generises.
(Neil Gaiman once wrote that trying to write a Lafferty-esque story was much harder than it looked. I have no reason to doubt him.)
Well, what Lafferty mostly wrote about was ordinary exceptional people under normal unusual circumstances. If that doesn't make sense to you, go read a few Lafferty stories and find out for yourself. Even his titles have a certain ring, from "About a Secret Crocodile" to "When All the Lands Pour Out Again," by way of "Le Hot Sport," "Nine Hundred Grandmothers," and "Slow Tuesday Night." You get the idea. Or maybe you don't, in which case I'm afraid there's no help for you at all.
Weirdly, the closest thing I can think of to compare Lafferty to is Charles Williams, the "third Inkling," but it would be a Charles William on laughing gas. As with Williams, theology, philosophy, and other Deep Things lie beneath the surface of what appear at first glance to be pot-boilers. But where Williams was, sometimes ploddingly, serious about the pots he boiled, Lafferty never seemed to take anything (except for everything) seriously, least of all his own self and his undeniable talent.
He was very Catholic, historically deep, and etymologically unique. There will never be another like him.