Yep that looks like poop to me. But it looks a little runny,it should be a hard, round ball. The lettuce might have caused therunniness. Just a pointer- rabbits should not diarrhea. Diarrhea iscaused from bad food or an unhealthy rabbit. Also, pleeease pleaseplease get the rabbit some hay! Hay is really important for rabbitsbecause of its fiber. Without fiber rabbits can be unhealthy and aremore prone to hairballs, which can be deadly. So if there are no petstores with hay nearby you can go to petsmart.com and get hay and othersupplies for it. For a happy rabbit you should get a couple toys like ahide-out (which is at petsmart.com too) and a chew toy. Also forrabbits to be happy they need to be taken out of the cage for exerciseand play for about 2 hours a day, or less if you have a very largecage. If you need more information this site and many others can helpyou keep your rabbit healthy and happy. Before i got my rabbit iresearched on rabbit care for about 2 months and i also bought abook.They helped LOADS, and if i didnt do all that researchi'd probably have an unhappy, unhealthy,or maybe even deadrabbit.Good luck with him, hes really cute!
P.S. In my opinion he looks a lot like a mix. I'd have to sayhes a Holland Lop and Netherland Dwarf cross. His face definetely lookslike a lops, but he has upright ears.