He has a point; if the MacBook is not recognising the internal keyboard, it's clearly a defect from the water damage. If the keyboard and/or trackpad are not working, as well as having dialogue windows popping up asking for keyboards to be connected to back up this idea, then I'd say that's something to worry about seeing as the computer is not functioning properly...
Well, yes, of course the water damage and the malfunctioning keyboard/trackpad is "something to worry about" but I was obviously specifically talking about the bluetooth window that was popping up that the OP was also worried about.