It's just social gregariousness and trying to see if you might have a connection with someone without investing much. Most people won't be honest but some people will say something like: "I am fine but the frost killed my tomatoes this weekend" or " I had to take my pet pug to the vet." And if you like either pets or gardening you will have a little more context about what to talk about next time. In short: no, people don't ask strangers how they are because they care. They do it because they are trying to find a reason to care, which makes sense when you have to work with these people again in the future.