I think you might have popped off the vent. There is a smallish vinyl vent hose that goes from the tank to the filler port. If you fill too quickly one of the 2 ends can pop off and leak. I had mine come off and had a leak into the belly.... The vinyl usually does not split or crack, rather a clamp comes loose.
I know on my Classic, if I insert my fill hose into the fill port too far, I get a tremendous venting of air out of the little vent hole to the point it will actually whistle. I figured out if I back the hose out a little, I have less escaping air from the vent tube, thus a lesser chance of popping the vent hose off the tank, or fill port. I had the factory tell me that they have seen owners be able to fill the tank so quickly that despite being vented, the tank can crack on the top from the pressure of rapid filling!! BAD
I hope this helps!