I think you can describe it as being in a foreign country, you are doing a tour at a tourist attraction and you ask for a guide who speaks your language and/or is from your country. I think in a way you can compare it to a cultural thing. Being from the same culture your guide will understand certain subtext. You have something vital in common.
I do not think Disney has a database, but I do think there are plenty of people open about their orientation at Disney. Disney offers products and services that are well-loved in the LGTBQ+ community, is tolerant, supportive, so LGTBQ+ people will want to work there. Same like the theater and airline industry are work places where often people can find a lot of support.
People who feel supported by their employee and colleagues will probably feel comfortable to share details about their lives, like if they have a partner or maybe saying to go to a LGBTQ+ bar after work, looking forward to gay days or pride. That is how "common knowledge" starts.
I know of most of my colleagues their relationship status, because we feel comfortable to chat about this during lunch.
I assume that the planning department of the vip tours know their guides. I do not think there is a box to tick in their system to select all LGTBQ+ or straight guides. I think the system selects a guide based on availability, and that there is someone manually reviewing the request for anything specific and then check if the guide and the group are a good match, and make adjustments if needed.