I don't think the airline was nervous. They just knew that the media would pick up on this and lambast United for being dangerous.
I would seriously doubt that the FAA would allow airlines to install electronic equipment on aircraft that would allow unfettered access to airline systems. Every piece of equipment on a commercial airliner must be certified by regulators. They don't just head down to Radio Shack and throw something together.
United was right, this guy was trying to exploit United's reputation without any basis of fact (his tweets show his ignorance of how things work) for his own financial benefit.