That does look like jelly poop and possibly brown diarrhea next to that. If you haven't been to the vet yet and/or your rabbits poop isn't back to being normal round fecal balls, but your rabbit is continuing to produce watery or pudding like diarrhea, and/or more jelly poop,
please get your rabbit to the vet immediately to be seen as an emergency!
https://rabbit.org/vet-listings/
True diarrhea, where it's not just a one off occurrence of some minor small amount of wet poop and then the poop returns to normal round fecal balls, and/or there is the continued production of jelly poop, are both considered an emergency. True diarrhea often is an indicator of something called enterotoxemia, caused by the clostridium bacteria and can be fatal in a matter of hours. Treatment is cholestyramine, metronidazole, and fluids. The continued production of profuse amounts of a jelly substance with little to no real poop, can be an indication of epizootic rabbit enteropathy, another fatal illness. Though there is no known cure, administration of the tetracycline antibiotic, cholestyramine, and sub q/IV fluids could possibly help. Either way, both are critical illnesses that require immediate vet intervention to have any chance of the rabbit surviving.
Medirabbit (bacterial/mucoid enteritis)
If your rabbits poop has completely gone back to normal and your rabbit is acting completely normal, there is the possibility it was a one time minor upset and your rabbit will be ok. Think about anything new your bun ate that might have caused this GI upset and I would stop feeding that if so.
When in doubt whether your bun is ok or not, it's always best to get your rabbit checked by an experienced rabbit vet right away. And if possible, bring a sample of the abnormal poop with you for the vet to check.
