Lord Surya in disguise of Sage had a smug smile on his face as he announced the "compensation" for making Gandhari worried, Which was the foremost and the strongest Mantra (Chant) there is, The Gayatri Mantra.
This mantra is so powerful that it even says that even if you don't know any other mantras, Chanting this mantra will be enough without offending others gods as this place is given to this Mantra by his lord, The Shiva god of destruction.
But that is not why he has a smug smile, the reason he has a smug smile is that this mantra is also dedicated to him, Which means once someone chants this Mantra, He has to bless them and hence he can see the person he was blessing.
Blessing is also a form of reward of Karma, The one of the few things Curses could not affect that much, In theory one can counter curse with his own Karma but that is yet to happen.
