Yeah it's silly no matter how you look at it. If you listen to Ben's presser today, they were a bit worried when the Browns signed Sammie Coates a week or so before their matchup. Coates was in the room for what, two seasons, knew everything there is to know about the Steeler offensive calls, hand signals etc. including their gameplan vs. the Browns. So they tweaked things slightly and went on with their lives.
To think Deebo would have even an ounce of new info to give Belichik is a fairy tale. By the time we play them again, if the Pats even make it that far, the entire gameplan, audibles and hand signals will be customized to that week's matchup. Anyone making the argument that Harrison is 'giving away the Steelers playbook' is simply delusional.
At the end of the day, the Steelers had no role left for an aging & slow Harrison. He wasn't happy about it and wanted out. The Steelers paid their respects and let him go. The Pats have huge holes in their D, so they're taking a flier on him. Probably eyeing a match-up with the Chiefs, hoping Deebo still has enough in the tank to make a dent against that waist-bender LT. There is nothing more to this story. Well, maybe that Belichik knew he'd get a rise out of a certain faction of Steelers fans. Those that are emotionally wound-up a bit too tight and push the panic button at a moment's notice. And those, of course, that have a bone to pick with Tomlin and the organization. Other than that, it's a drop in the ocean story with little to no impact in real football terms.