"Quite big and powerful army, Why do they stand like that? Should I destroy it or just create protection around Hastinapur?"
Karna appeared on the border of Hastinapur and saw the big mighty battalion filled with unyielding warriors standing firmly on it but facing the opposite side of the entrance of the kingdom.
This made him confused as to why nig only this army was not marching forward here but standing facing to the other side of the border not caring about the retaliation that will definitely come from Hastinapur.
So Karna thought of two possibilities, Either the other party is too confident in their power that they don't care about the counter attack from Hastinapur or they know Hastinapur would not attack them.
First one is too foolish for Karna to even think it would happen, He only took it into consideration because it's a common thinking process. After all, a big army like this knows the power of Hastinapur.