It's an interesting phenomenon. I see it when riding my bicycle and motorcycle. There is a need for some to want to connect, with either a wave or a hello, to others that are performing the same activity. Do we do that when eating ice cream and spotting someone else eating ice cream, when scratching our nose as we lock eyes with another nose scratcher? If you are a social person then make contact. If you are not then don't. Just don't get upset if the other person doesn't behave in the manner you think they should. If they are giving you a reply out of an obligatory politeness without any true feeling then it is just an empty gesture. It turns into a mindless task like when people say, "Gesundheit" or "Bless You" when someone sneezes.