And for him applying as a single person also doesn't make sense. (that's actually the wrong term. Once he's married, he can only be separated or divorced. He cannot be single again.)
Not saying that any of this makes sense, but it's possible the 'applying as a single person' means applying under whatever program as unaccompanied by spouse + dependents. That is reasonably common - the spouse + dependents would be examined medically (and I assume background). If done this way, the applicant can apply to sponsor them once in Canada as a PR.