It could be coming up to a shedding cycle. Water softens the skin and helps with shedding, and snakes will actively rub against textured surfaces, like the arm in this video, to work the old skin loose. That would explain both the rubbing and its tolerance of the handler. The cool water may also just feel good on a hot day, since snakes are ectotherms.
While we like to project our emotions onto snakes the way we do with other animals, snakes are fairly simple compared to mammals, and there's no real evidence they form social bonds the way a dog does. A snake can be seen preferring one handler over another, but that's usually closer to comfortable tolerance than genuine affection. This one is likely habituated to people in a captive setting, so it doesn't read humans as a threat. That relaxed, approaching behavior gets perceived as enjoyment when it's really just a snake that feels safe and is getting something useful out of the contact.
Or it could just be a good snake who wants pets and we should love it and care for it and give it all the frozen mice it wants.