I have been specifically and repeatedly told women at work don’t want flirting or any other interpersonal interactions. So that shit is shut completely off when in public.
Without being there it's always a guess. But putting "You know" at the front like that is pretty damn explicit. She wasn't just making a random comment. That's like movie trope obvious.
There are always outliers though, she could of had a brain fart, or he could have said something to make her believe he felt she was working late.
That's when you ask things plain and simple. One of my exes was the manager for a fast food joint and at the end of her shift, sitting at my table and kinda chatting away. At some point I simply asked her "so are we going back to your place to make sweet love after that, or what?" with my french accent on full blast. It had the desired effect of making things clear.
I wish I had had the balls to do that more often in my life!