That does actually seem wrong. Whatever the reasons for the kick, if the player isn’t present at the kill, then they haven’t killed the boss, simple as.
By the same token, when some scrub pug quits a key on the last boss and the others 4-man it, they should not be mailed their loot, nor get a vault slot…
Unfortunately this is a scummy practice by some leaders. We’ve even had reports of a group of five being removed and not only have no access to loot but are also loot locked.
You should just call it a distasteful and an obnoxious experience and move on. I’ve known many people in Warcraft. I’ve always been a PUG’ger both in Classic and Retail—I’ve seen raid leaders like that many times, while some gave people more than a couple of chances, see if they can improve or it was just a technical issue on their end. (I’ve, at times, had technical lag issues, etc., myself.)
As for the loot, it’s pretty sadge. I would basically put that raid leader to the block-list so that I don’t join their PUG’s again.