I'm sorry that happened to you. Something I wish people would bear in mind when it comes to LGBT people... we're just people. So by that metric, some of us are lovely, some of us are depressed, some of us are angry, and some of us are shitty.
We're not shiny magical rainbow people, just humans with the same flaws as everyone else. You'd think someone who had suffered hatred & persecution would not inflict it onto someone else... but sadly, some people are just shitty. You had an interaction with an exceedingly shitty human being who happened to also be LGBT. Please try not to let it influence you, or prevent you from meeting awesome people at future events!