Baby shaking head

My 4 month old found it hilarious when his dad would shaking his head to say no no no and would copy him killing him self laughing whenever dad done it and would copy him and repeat… now my baby is doing it when he’s protesting going to sleep at night and for his naps… has he learned to copy dad with no no no shaking head and has put two and two together or should I be worried the head shaking is more sinister?