Well, I won't say where I am in the story since I don't want to spoil anything but after a certin part of the story I was running across the Wasteland and suddenly I came across something I've never seen before, a Deathclaw. The thing was, it had bairly any heatlh. I shot it once with my minigun and it just dropped. 

Yeah, that's the infamous Deathclaw Launch. No, I just made that name up.
But I noticed it, too. I came across some Enclave camp and suddenly a Deathclaw flies right off the screen. I think it happened about 5 times during my first playthrough. Oh and btw, they come back down. At least that one did while I was looting that camp. It came down right behind me and ripped my head clean off.
I guess it has something to do with them spawning in an occupied spot, because there was a metal pot lying around where it launched. But that doesn't explain why it only happens to Deathclaws. Yeah, I don't know.

Never seen that, and I've killed about 20 deathclaws today alone lol.

Well, sounds to me like your one lucky SOB. Im usually forced to deplete copious amounts of ammunition and weapon strength trying to kill those bastards. For once, theres a glitch I would like to encounter.