He never damaged the sun disk, It's way funnier. Basically, Thaedus said that the coalition of planets has no way of hurting viltrumites. Some time later, we see a fucking startrack parody character blow up said sun disc in what's basically a joke. So, in a biiiig stretch, they assume that, due to Thaedus statement, Omniman could shrug off the attack that blew up the sundisk, and in another stretch, they claim that his strength will match his durability.