it could literally be a product of having the wrap on and retained heat (particularly if it was a warm day). If there were remaining infection, he likely would not be sound. Watch the leg carefully, check for a bounding pulse and any resulting lethargy that may arise. This may be additional infected areas re-abscessing. Try to keep him quiet until he has adjusted to being out again, check for the bounding pulse, keep an eye on his overall temperature as this may be an early sign of compensatory issues. The good news is that by the time your vet is available to follow up, he shpuld have resolved or a continuing problem will be more obvious.
Best of luck with your horse, SusieL, MS