It isn't a question of if he acted alone but rather if he was the leading advocate. If within the organization it was seen as primarily his idea or its leading proponent then he is stuck with the blame for its failure. Given how much he both advocated and defended the move then I would say he owns it and will be the one to primarily suffer the consequences for its failure.
I find it more than curious that many NESN analysts such as Remy, Eckersley and others have politely panned it. I suspect they wouldn't have said a word if the idea had been thoroughly embraced at the Henry or Werner level of the organization. I suspect the latter two approved it because coming off the title they had little reason to doubt the manager's judgment until its error was demonstrated by subsequent events. For this reason, I suspect that the manager has lost a lot of credibility with ownership, hence Henry's subtle warning.