It could be all the possibilities you mentioned. Too many superworms, too many grapes, handling too much and if you did feed too close to lights out or the basking temps are not high enough, all of these can cause regurgiation.
I would not offer any food for a day, just water, separate the two dragons so you will be able to tell which one is regurgetating in the future. After they had a day without food, offer greens, no fruit (too much fruit isn't good for draogns, they should only get a very small amount on their salad. A single average sized grape, without seeds, chopped up, is more than enough fruit per serving.) and no insects.
If they are eating greens and neither is sick for a couple days, then there shouldn't be any further problems. If they keep throwing up, or one does, double check temperatures. If temperatures are fine but if they continue to regurgetate I recommend taking them to a vet to treatment.
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PHLdyPayne