Moreover, I have never heard fuel dump described as a "vent".
Me neither.
This probably belongs in Snopes as an urban myth - the OP's post isn't original, by the way, but is lifted from a 1998 newspaper article about the accident by a French-Canadian journalist (Paul Koring) on the Toronto Globe and Mail:
Could the pilot have landed the plane?
In fact the TSB report, which of course includes data from CVR and ATC recordings, doesn't contain the word "vent" at all in the context of fuel.
its my understanding that they hadn't begun the process because the smoke (and eventual fire) on the flight deck became a bigger priority
Maybe - but the report does say
"Coincident with their declaration of an emergency condition, the flight crew indicated that they were starting to dump fuel and there are indications that they did so."