I know we're all guessing in the absence of clear information, but I wouldn't think Tom Evans would be "paid off." I think it far more likely that the hospital gave him an ultimatum:
- get your supporters to back off,
- disband "Alfie's Army,"
- stop giving interviews
- call off the press
- cease all legal actions with UK or international courts,
- be sweet and say nice things about Alder Hey and the NHS,
... and if you do not, you will never see your son alive again. We can do that. We may not even give you his body.
Simple as that.
That's my guess.