But it's often used for specific cis people when you are trying to create a detached or dismissive tone about those cis people

No? I’ve never seen that before and it seems like you’re making this up as you go.

The above poster used "Their awkwardness" as well which isn't a confrontational use of singular they and establishes a habit for distancing themselves from using the known correct pronouns.

In the trans community this is sometimes known as "The coward's they". A soft form of transphobic behavior that refuses someone's gender when a trans person is well known enough or their gender is self evident by their presentation and behaviour but the person referring to them really doesn't want to use the correct pronoun. Sometimes it's a not intentional thing the brain does when outright transphobia mashes up against the brain coding someone they see as passing so "they" starts getting used so the speaker doesn't trip up and accidentally use the correct pronoun. When done intentionally it's designed to be subtle enough to not be caught by people just on the outside edge of trans inclusive communities but to trans people and their nearest and dearest it's usually pretty obvious. Basically a dogwhistle.

You do not need to be a white knight for this person by trying to pour over their diction to try and find some pretext to defend them. Challenges to a coward's they are usually no more than a reminder of a person's actual pronouns. Short and sweet and over with quickly. Either the person gets the hint or they don't care. It's only when this response starts happening that people think using "they" dismissively to trans people works the same way as using "they" dismissively to cis people and the coward's they finds the camouflage it needs to live on because even if this was not a coward's they it functions exactly the same to a trans listener.