Foolishly let stray rooster mingle with my flock
Is the rooster showing any sign of illness? Normally a new bird is kept in quarantine until it's sure they are healthy, that being said, I didn't do that with my own rooster and things turned out okay. Beginner's luck?
Judging by how your rooster acted, putting him in with the chicks was the best thing for him. Only time will tell if it was detrimental to the flock. Good Beginner's Luck to you too!!