Rabbit’s can’t vomit, so it wasn’t vomit. Sometimes rabbit pee is thickish because they pee out the calcium they don’t need. Most other animals poop out extra calcium, but rabbits are different and their pee is often cloudy and the urine can have many colors, yellow or orange isn’t uncommon.

Is his appetite normal? Is he acting normal? Those things are what you want to keep an eye on, esp appetite. A sick bunny doesn’t want to eat or only eats very reluctantly.