Calling Muhammad a terrorist is really a special amount of Islamophobia.
Muhammad had between 400 and 900 POWs of the Banu Quraish tribe beheaded. Not calling this terrorism means twisting the very meaning of terrorism into pretzels.
I doubt you'll find many historians calling the Massacre at Verden terrorism, for instance, despite executing 4500 prisoners.
It is a matter of linguistic taste if we use such word in medieval context, but the principle is the same as in modern terrorism, and jihadists of the 21st century explicitly say that they are motivated and inspired by Muhammad's acts like this one.