While this may sound cynical, I've learned the hard way that just because we're all under the LGBT umbrella together doesn't mean that we trans-identified people get the same amount of respect we give the lesbians, gays, and bisexuals (though bisexuals seem to be more understanding because they are also marginalized by the other two a lot), whom we reasonably consider brothers and sisters in the same struggle for acceptance, understanding, and equality. Not all of them, but there's a large number out there that's just big enough to be worrisome.
I'm a member of several LGBT (LGBT News, Wipe Out Homophobia, etc.)groups on Facebook, and whenever there is a pro-trans-man/trans-woman post some of the members turn very transphobic. They turn around and bully the trans-identified and their supporters and say horrible things to them. It's the weirdest thing. You'd think a group of people familiar with ignorant, unfounded hate wouldn't be so quick to turn around and hate on others struggling just as they are. But they do. It's irony; they demand an end to homophobia and want people to accept them and understand them, yet they behave towards the trans-community the same way homophobes behave towards them.
Even my own lesbian aunt, whom I've always supported without question or judgement, looks down on me for being a transman and refuses to discuss it with me or even acknowledge it. She thinks because she never saw it before (because you know, the whole time I was a teenager and young adult dressing like a male and acting like one didn't give it away), that it's not true.
So, who knows. Maybe this person made a mistake, or maybe they were being transphobic. Either way, if you're in an LGBT center, odds are you have more allies than not present, so don't feel like you can't just say, "Excuse me, I am a man. Please use the proper pronouns. Thank you," if someone tries it again there. Happy trails, and I hope all goes well.