Yes, it was a cool piece of artwork! There was a water taxi facility right next door! I'd like to try riding it once too. If I get the chance, I'd like to take a photo! water-taxi.tokyo/
If there is no phone in the room (to call the front desk), there is usually one in the elevator. Probably they don't have one in each room because they would get too many inquiries.
As you said, there was a wrestling event going on that day. The hotel was large and had suites, so it was right in front of the venue, so there was a good chance they were staying there. There was also an APA Hotel Tower in Ryogoku. It was for events.