Can I meet an adversary 100 kton ship in my space? Yes.
Can they call it as battleship? battle cruiser? heavy cruiser? cruiser? escort cruiser? carrier? freighter? giant freighter? or what ever other way? Yes.
Is this classification meaningful respect the role this ship can have in the fleet? Frankly, no. IMO, its systems, weapons, armour, shields, etc. are much more meaningful, maybe together with the knowledge whether it is a military (M) or a civilian (C) ship.
If my sensors warn me about this large ship, I can be really suspicious it can be very dangerous, even if I don't know whether it is M or C (I can think a cargo loading troops and deploying them where I am unarmed).
So, IMHO, a ship classification can be a very secondary information.