There are differences in nomenclature regarding firearms.

A cannon is a large bore piece in a shore battery.
That same piece aboard a ship is a Gun.

A hand held piece is a Pistol. (From the Italian meaning pipe)

A smooth bore long piece is either a fowling piece, (For shooting birds) or a musket for shooting other people.

A rifle is a long piece with rifling in the bore to make the bullet spin. These are much more accurate than a musket. During the revolution the British soldiers carried muskets which were good for about 50 yards. The colonists had Kentucky rifles, (actually made in Pennsylvania) which were accurate to two hundred yards or more. We all know who won that difference of opinion.

Anyway, I digress, that teacher was not dead right, what he had was a rifle. It is only a weapon if he shoots someone, or means to.

Rant over.