Abusing vote to Kick
They wanted 80s. Not because of experience, but for stats. A 78 with have lower stats then an 80. That’s all.
There are plenty of dungeon groups that allow sub 80s (I join them, if I want a certain dungeon/path for tokens, I don’t care on the levels, my guardian is set up to handle most things, I just want bodies so it’s faster).
The clue was in their LFG text. They said they wanted a quick run which usually means they are looking for geared players so they are likely to be the sort of players who will want to see your gear and build. So the 78 will have been like a red rag.
I’m not saying it’s right but that’s how some of those folks are. Insta-judgement, insta-kick.
Maybe start your own party and make the 78 thing clear in the lfg text. You’ll get plenty of players.