I want to say that I speak French but I'm not francophone, so I'm not an authority on the intricacies of the French language.
When we sit in a drafting room and we draft, we try to achieve the clearest way of expressing the same thing in both languages. Sometimes that means using different words in each language because of what the words mean, respectively. That's what happened here.
We have assured ourselves that the meaning is the same, and that it is expressed clearly in both languages. I believe that “actively expressed by conduct” versus “affirmatively expressed by words”, was just considered to be a better way of expressing the concept of positive action or words, because one adverb fit better in English with words and the other with conduct. It's as simple as that.
I want to stress the fact that the two versions have to be read together, and their objective is to codify the principles in the Supreme Court of Canada jurisprudence, not just in paragraph 49 but also in the other locations that I noted. The words are carefully chosen to reflect that.