someone I didn't know

Life On my way home from work yesterday, first day back at that place, very tired, it's warm for once, and as I reached the bus stop, a girl passed by on a bike. She grinned at me, and said "Hello!" brightly almost knocking someone over as she turned around. I smiled enthusiastically and waved and said "Hello there!" back and we asked each other how we were and then she was off again down the street. The whole exchange took seconds but the effects have lasted much longer because ...

... I didn't recognise her. No clue. When this has happened before, I've usually been able to work it out in retrospect and then wished I'd remembered to ask them about this, that and the other. This time, nothing, and I've a horrifying feeling that I should know them really well, that they might even, eep, read this blog. The other problem is that, well, I have a weird feeling they weren't in fact saying hello to me, but perhaps someone else who was at this packed bus stop and I was the loser saying hello back to someone I didn't know anyway ...