Looks like a regurgitation. The foul smell you encountered is par for the course for those little nasties. As far as the length of time between the first and second attempts, it certainly could have played a part - especially since it'd been thawing for a fair amount of time before then.
It sounds like your husbandry is on par, so that's out of the equation. For you, the best thing to do (after you clean up the grossness) is to be extra vigilant in your observations over the next couple of weeks to see if there are any additional signs of something larger going on. Keep handling to a minimum (necessary tank maintenance only) and make sure his water bowl stays full and clean. Once a couple of weeks have passed without concern, you can offer a meal again. Make sure it's one that's quite a bit smaller than his usual size to give his digestive system a chance to ease back in to things. Regurgitation is a pretty traumatic thing to happen, but doesn't have to be something that should loom over your head as a concern as long as you take the proper steps afterwards.
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