When you encounter someone weaving from side to side, and not making a lot of sense, at 2am in the middle of nowhere, then making conversation to judge their state comes under the heading of 'duty of care'.
Some encounters are interesting for both parties, and you end up making a new friend. Others result in the person you've spent time reviving riding off into the night, just as you hit a slump yourself.
During daylight hours it's likeliest that you'll end up conversing with someone who matches your pace. In my case that tended to be tandems. The usual scenario being that I'd been dropped from a group on a hill, started to drift as I tired into a headwind, and tagged onto the wheel of a passing rider, or tandem.
Solos quite reasonably expect you to take a turn on the front once you've recovered, tandems often don't. Parasitic wheel-sucking is a bit embarrassing socially, so pulling alongside for a bit of a chat is normal.
Audax is unusual, as participants come from a wide range of backgrounds, and from around the country. It's normal around here to chat at supermarket tills and bus-stops. Visitors from other parts of the country sometimes ask where you know the stranger you've been talking to from. They're a bit perplexed when you say that you've never met them before.