Airline pilot here, with experience with both systems, but not technical knowledge of the inner parts or how much they are capable. I have to leave right now, I´ll be expanding this comment a bit latter.
By now just tell you that both systems are capable of creating great troubles if they can be accessed as easily as he claims (and I think they are).
A pilot probably wouldn't know how all the systems work together. (They probably know what ACARS and ADS-B -do-, but not the implementation details.) You would want an avionics engineer--so someone who works at Honeywell, Rockwell-Collins, Garmin, etc.
If you can access the wiring in the aircraft, especially with the new fly-by-wire stuff, you could cause problems. None of the communications are encrypted (as far as I know), because it's pretty much assumed you can trust what's on the a/c buses. Also, redundancy helps get rid of erroneous data when it only shows up on one bus.
I don't know much about ACARS and ADS-B. While it wouldn't surprise me if there were problems, we also tend to notice rogue transmissions in our spectrum. Much more quickly than people realize.
I'm rather doubtful that the actions presented in this article can be done in that manner.