What does "gatekeeper" even mean in this scenario? There was no employment relationship, no ability for either party to fire someone or impact pay or job responsibilities.
And is "exploiting" synonymous with "having sex with"?
You seem to be saying two people in the same community can never have sex, because one or the other will have more power within that community making it exploitative.
If not, are the circumstances where it's not problematic?
When you're a new member of a community, you're dedicating a lot of effort to working out its norms and customs. How frank are you in giving feedback? Is it OK to swear? When is it appropriate to go out with the group for dinner or a round of drinks? There's no right or wrong answers to these questions, so you can't reason about them from first principles; you just have to learn by absorption what the community finds normal.
As an established member of the community, especially one who routinely organizes events for it, your actions heavily guide that process of absorption. So you can't sleep with anyone in the community until they've been around long enough to understand that the sex has nothing whatsoever to do with community norms. It's not just about whether they think they have to; they have to know that it's not a default, that it's not something a typical community member would do in their shoes, that nobody's going to think they're weird or a prude for turning you down.
"Why would anyone think that in the first place?" There really are communities, including big ones that organize events, where sexual access is part of the norm. Everyone knows what's up when a rock star invites you to share his hotel room. You and I understand that the analogy to a programming conference is ridiculous - because we're deeply acculturated into what a programming conference is and what kinds of things are or aren't normal at them.