If I was out riding along on my bike, either for exercise or commuting, and I crossed paths with a family out for a ride, normally it wouldn't occur to me to have any interaction with them. I'd assume they're busy keeping an eye on their kids, or doing whatever they're doing, and that some random stranger passing by going about his business (me) is just part of the background scenery to be ignored. If I noticed one of the parents acknowledging me I'd nod back, but I wouldn't be watching for it, so I might be lost in thought and stare right through them without noticing or even realizing I was being rude (in their eyes).