This is a really interesting statement. How would someone discriminate against someone who is LGBTQIA+ without knowing that they were or not? LGBTQIA+ is not something that can be recognized right away like skin color.
To say nothing about things like "passing" in the trans community, or stereotypes about gay men and lesbian women.
Different minority groups get different results from phone call inquiries by voice, because they have distinct linguistic patterns not present in General American English. LGBT people also have their own distinct patterns, though not all LGBT people use them.
Also, some visual markers are probably present in the gay population at a higher rate than the general population, like earrings, dyed hair, or wearing clothing not tied to their sex.
Even for non-flatmate scenarios, some landlords are remarkably nosy. Also, in many jurisdictions trans people may have legal docs in a name they don't use anymore... the list goes on.
It's also reasonably common for people to be discriminated against because people _incorrectly think that they are LGBT_, incidentally.
I’m assuming one doesn’t want to learn their flatmate is a raging homophobe the first time someone of the same sex is brought around.
It's best to read things in good faith. On the whole, people on HN do try to be helpful.