I was told this yesterday and it doesn't sound right to me, particularly as the next thing to be asserted was that Trudeau feared the British Privy Council might make a similar ruling regarding Canada's Aboriginal People if he did not act first.
I had thought the Privy Council no longer had authority over the Canadian Supreme Court after the Famous Five" case of 1929, but that's me remembering tour guide information, which is often suspect. Also, I had thought the Charter was more political grandstanding than anything else.
So what was the national and international context surrounding the creation of the Canadian Charter of Rights and Freedoms??
Honestly that explanation seems to discount the very-Canadian problem that until The Charter, our Rights and Freedoms were enshrined in a very vulnerable Bill of Rights.
Like any legislation, its incredibly easy to amend. Its not entrenched, and that's part of the reasoning behind entrenching something very similar to this Bill in the Constitution Act - Namely, the Charter. This is undoubtedly at least part of the national context surrounding the 1982 repatriation.
You're also right on the Privy Council no longer having jurisdiction. It was officially removed from the hiearchy of the Courts in 1931 via the Westminister Act. Until that time, Supreme Court decisions could be appealed to the Privy Council. IIRC however, no appeals to the Privy Council had been made since 1929, as you remember. This is not the explanation either, therefore.