Yes, I understand the distinction. The slippery slope argument assumes that the distinction is a particularly important one regarding how the law is applied in practice. Read a couple of the cases on OHRCs site if you’re interested in seeing how they handle evidence in discrimination cases. When senators and the Canadian Bar Association and civil rights lawyers weighed in on this their arguments often centered on how evidence of discrimination is understood in the context of a case that results in material harm.
And again, the Peterson argument also assumes that OHRC rulings on this exact point become the basis of C-16 enforcement, which is probably the weakest link in the logical chain.
FWIW, Peterson also skips or waves away things like balancing tests in making rulings, which also came up in the debates. Which is to say enforcing the law can’t violate someone’s free speech or religious rights, either.