TDF did belt, torqued up normally, possibly to the looser of the two specific figures, as no charger on the engine.
You fitted a charger afterwards, and at the time didnt then increase the torque on the bolt to give it a better chance of survival (ie the higher setting Dan mentions)
Then it failed.
If I was TDF I would be amazed if someone pointed the finger at me in those circumstances TBH, you did the charger install, and its almost certainly as a result of that extra strain the bolt undid.
Did whoever you got the charger off explain to you that it puts a lot of strain on the pulley and that you should check the pulley torque as a matter of course when doing that sort of thing?
Not that its their responsibility TBH, if you werent aware of the implications then it shouldnt have been you doing the work, it should have been someone who knows about such things and hence would have made sure that bolt was really well torqued up.
Sorry if it sounds harsh, I really feel sorry for you that it happened and I am glad you are sticking with it not giving up and I hope it all goes well with the rebuild, but ultimately this is just one of those times when you learn from your own mistakes IMHO