I don't like "outing" people, in case they didn't want their presence at an event to be widely known
I understand where you're coming from, but in the present context this is consideration bordering on madness. Trevor is one of the founding Y Combinator partners. How on Earth could it be "outing" him to note that he was at Startup School?
I never assumed that every YC partner would be at every YC event. As far as I'm aware Trevor wasn't organizing Startup School, merely attending it; and PG (for example) didn't seem to be there at all beyond his appearance on stage.
I wouldn't say that Trevor was trying to go incognito, but he certainly didn't seem to be trying to make his presence obvious either.
I understand where you're coming from, but in the present context this is consideration bordering on madness. Trevor is one of the founding Y Combinator partners. How on Earth could it be "outing" him to note that he was at Startup School?