Here's, a thought (and, it's total speculation). Assuming this is a real story, maybe Clemson's argument is premised on the idea that by adding Stanford, Cal and SMU, the ACC devalued its brand, rendering its current GOR unreasonably punitive or possibly even unenforceable. This might explain why Clemson, FSU and UNC (the three schools most vocal about their desire to leave the ACC) really voted "no" on the additions, despite the fact that they were presumably added precisely because they would temporarily increase revenue for the current members (thereby addressing the primary grievance with the conference).
Had Clemson, FSU and UNC voted in favor of expansion, it would have undermined any claim that adding schools devalued the conference over the long term (and the ACC's contract with ESPN runs until 2036), despite any short term increase in revenue. Anyone voting "yes" would have been complicit. By opposing expansion, they're in a far better position to claim that their fellow conference members made a mistake to the financial detriment of all, but justifying more favorable terms for conference departure for those voting "no."
How funny would it be to find-out that Clemson, FSU and UNC not only didn't truly oppose expansion, but secretly welcomed it for the opportunity that it could create to attack the GOR. Under such a scenario, they just couldn't publicly advocate for expansion themselves. Instead, they had to wait for some dupe to step-in as an advocate for adding schools, let other conference members go along for the ride and vote against what they really wanted all along. Of course, in this scenario the dupe would be Notre Dame, a school with a proven ability to string-along fellow institutions to their eventual detriment.
No single school had a greater hand in the ultimate demise of the Big East than ND (when they bolted for the ACC, any remaining hope was lost). And, of course, it was the ACC's poaching of Miami. VT and BCU from the Big East that precipitated all this winner-take-all conference realignment. Nothing would make me happier to find that ND unwittingly miscalculated in aggressively pushing for the addition of Stanford, Cal and SMU only to find that it was the trigger to destroy the ACC as we know it. What goes around, comes around.