I experienced something similar on Gamejolt - one game in particular that I hosted there suddenly started getting hundreds of plays per day, about a week after I published it, without me really doing anything to promote it. Unfortunately their analytics are not as good as here, so I was never able to tell where the traffic was coming from, which was really quite frustrating. I think their forums are more active than here, and it might have been that somebody posted my game there, but I didn't think to check at the time.