Rough-housing is fun physical contact.
Abuse and negative characteristics are often at the root of bullying behaviour
As your ds gets older, ensure that you explain that these rough and tumbles are restricted to his house and with his daddy.
Dh and ds1 engage in daily rough-housing.
Ds1 is almost 3 and this has been going on since he was about your ds's age.
We've yet to see any evidence of bullying behaviour. In fact, he is one of the most empathetic and sensitive 3 year olds I know.