Chretien was instrumental in the authorship of the Charter, signed the Proclamation of it alongside QE2, and is still alive.
The website's way of phrasing that is misleading, even if partially true.
And to further illustrate your point... The greatest authority on post-1982 Constitutionalism in Canada wasn't a politician, but a legal scholar, Peter Hogg. Sadly, he died in 2020.