If he says we must separate from the conciliar church, then by definition, the groups you mentioned are not among those “faithful to tradition,” since they have not separated from it.

No, that's the contradiction.  He advises people that, if their diocesan churches are contrary to the faith, then they should seek out "Traditional Communities".  He doesn't elaborate.
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Further, in the beginning of the interview, he explains that it is not necessary to "separate from" the Church because of conciliarism, because the Modernists have separated themselves due to error.  So, he's arguing that one can be "under rome" and still a Trad.
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“While it is clear that no admixture is possible with those who propose adulterated doctrines of the conciliar ideological manifesto, it should be noted that the simple fact of being baptized and of being living members of the Church of Christ does not imply adherence to the conciliar team  (Comment:  He's saying that being a catholic doesn't mean you agree with conciliarism); this is true above all for the simple faithful and also for secular and regular clerics who, for various reasons, sincerely consider themselves Catholics and recognize the Hierarchy. “  (Comment:  So, for those that recognize the hierarchy -laymen, diocesan and religious clerics- they are not considered conciliarists just because they go to a diocesan mass.)