I like the idea of a shorter character limit as it nudges users to a specific mode of interaction: short thoughts/updates and not long-winded soliloquies. It's signalling that interaction with this platform doesn't demand much of your time or attention. I don't know what the about page has to do with it, but you have to draw the line somewhere.

That said, I'm not a social media user besides HN I guess.

For perspective: you just commented 404 chars. Your first paragraph alone was 346.

My comment on the about page was that it needed more than 280 chars to communicate what the app is about - even the title + intro exceeds the limit.

If it is truly believed that 280 chars is enough to communicate an idea, then the about page should follow that philosophy.