I assume anything I say to a "stranger" can come back to bite me even if I send it in a private message.

> What's public about a private message?

Is this the set up to a joke? Nothing. But so what?

You said that:

> ‘not looking but happy to chat’ was code for ‘yes I’m looking but not saying so publicly’

but this was in a private message, so why would this person be speaking in code?

It's literally on Twitter, isn't it?

No, the initial conversation was in LinkedIn private message. The OP would have had no reason to use "coded language that obscures my intent in public" at the time that they wrote that message (which was long before they decided to screenshot and publicise it)

The part not blackened when subsequently posted on Twitter.