I was thinking about that detail as well. We only know the white hair picture from the wanted poster in the newspaper but no details about 'Sun God'.

So there could be Shanks, last seen on Elbaf, who could know something and told the giants. Or we know there was also Jaguar D. Saul on Ohara, who knows about the void century. A friend of mine also mentioned Caribou, who was last seen on the Sunny in the barrel at Egghead, so maybe he was spying for them? Lots of possibilities.