Even if you know what gender the person is it's not uncommon to use they

"Well officer, I saw them walk from their car up to the door then they turned and looked around, that's when I saw them pull the ski mask down, draw their gun and enter the bank"

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Manager: What was the customer doing when you told them to leave?

Clerk: Well I had been trying to help them with their project but they kept stepping into my personal space, then he places his hand on me and that's when I decided they'd crossed a line and needed to leave

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Most people wouldn't even bat an eye swapping they out for he/she in conversation in person.

It would depend on context, if you ask me. The bank robbery was across the street & half a block down? Completely unremarkable to say "they". The clerk is complaining about sexual harassment, hand on thigh? Avoiding "he" implies a careful choice not to say, either to hide an identity, or because the customer was obviously confusingly gender-ambiguous.

I interpreted “they” in the second one as implying distance from the person in question, like the speaker wants nothing to do with them and is emphasising that they were a stranger. Possibly part of why saying “they” feels uncomfortable to people, but I’d never realised it until reading that example.

In my case if I don't know someone well, or at all, without thought I use gender-neutral terminology they/them/their and with pets and babies, again without thought, I naturally use it.