The word means actually that a weapon and NO greek modern or ancient historian has ever reffered to the shield as "Hoplon"...
Except the Liddell-Scott dictionary... which is the best and most acreditted source on ancient Greek...

Words come to mean other things over time.

Aspis is a general term meaning shield. A shield is an aspis.

Think about it, why do we call Peltasts, Thureophoroi, etc by the name of their shields. That was Greek naming convention. Strateot(eta)s was the term for a soldier, or 'man at arms'.