Exactly, from the other players perspective you just bailed on them.

While recently leveling my DPS jobs I often had to wait 20+ minutes when I was direct queueing for the one dungeon relevant to their current level.
So if you were tanking, you potentially had two ppl (the healer probably didn't have to wait as long for queue) waiting just as long for the initial queue into their dungeon run, then having to wait again for a replacement after you left without any explanation. It's usually not instant when waiting for Tank or Healer replacements.

You clearly have a colorful enough vocabulary, writing any reason in chat, even if it's a lie, would have defused the situation.
"I'm not feeling well"
"My PC is acting up"
"My internet is acting up"
w/e

And if you're accidentally turning off tank stance, then probably need to reconsider your button placements...