Do you think Goblin slayer really cares about that sort of technicality? She said it herself.
Actually yes. Guild Girl once gave him a quest to exterminate "sea goblins", only for them to turn out to be fishmen. Suffice to say it pissed him off.
Anyway he likely wouldn't see Suika as a goblin solely for not looking like what he's used to. Now the hobgoblins under Remilia on the other hand....
tbh it's also a stupid idea to mock him about "goblins" when there are no sign of goblins.
He knows what they look like and how evil they are. Those pathetic little, greenskins that are chaos incarnate- no wonder why Orks smash them at any given time.