These are statements I can work with. Yes, I also figure that Squardo isn't working by himself, and there's someone else he's been working for. Maybe it's a recently development, or he's planned it from the beginning. I've also considered Kaidou, but what bugs me about this is that Kaidou would have to be present at the war, and I wonder if he'd risk it. Who knows.
Gov't spy, Emperor spy, or other spy - I'd like to imagine that Squardo is working for someone so there's a bigger picture. fingers crossed
It's possible Kaidou managed to slip past Shanks', even if it's just by himself, leaving his crew to the battle. Shanks and Kaidou's crews supposedly have been engaged for a while now; it's not impossible that their conflict has already been resolved. Or Squardo could be to Kaidou what Gin was to Krieg… remember how Gin acted as a decoy by himself so that Krieg and his crew could escape, and ended up being captured by Fullbody? Perhaps Kaidou anticipated he'd be interfered against by Shanks, so he sent Squardo ahead as a Double Agent to stir up trouble.