Sugars swelling is edema. He thinks she is very close and very very large. He listened to her heart and breathing, but she was not being at all cooperative or ladylike and tried to kick the &^%$ out of him. It is very unlike her as she is a gentle plodder.
Was he trying to palpate her when she was making a fuss? That's not ~all that uncommon~ for a mare to protest that unless it's happened so much it's just part of the routine. I know she's had foals before, but if they've been pretty hands-off, she may view it as a very rude invasion.
So what about the Edema.... Edema just means a fluid accumulation doesn't it? cause?