And St Paul wrote to catholics and called them "saints".  You're making a mountain out of a molehill.

Similarly, in a Sep. 1, 2020 letter to Catholic Family News contributor Stephen Kokx, Vigano asserted firmly that “it is clear that no admixture is possible with those who propose adulterated doctrines of the conciliar ideological manifesto….”

So, the question now has to be asked: What happened to all that?! Now he is mixing not only with regular Vatican II believers but also with Protestants, Eastern Orthodox, and Jєωs, labeling them children of God, children of light, part of the church, and soldiers in God’s army!

I think the Novus Ordo Watch has misunderstood what Msgr. Vigano meant by "admixture."  He's not speaking of avoiding venues where modernists, Jєωs, Protestants, etc. will be present, but of avoiding modernist errors.

M. Brian McCall of the Catholic Family News introduced Msgr. Vigano's letter, with this explanation (which likely irritated the Novus Ordo Watch, and incited their response):

"Refuting Sedevacantists:
The Archbishop begins by clearly refuting those who have mischaracterized his prior interventions as advocating that Catholics break with the Church or refuse to acknowledge the occupants of hierarchical offices (as do the Sedevacantists). He delineates the need both to refuse any admixture with the Modernist errors and to remain firmly within the Church: “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; 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.“
https://catholicfamilynews.com/blog/2020/09/01/breaking-news-archbishop-vigano-responds-to-questions-posed-by-cfn/ 

Or does the Novus Ordo Watch think Msgr. Vigano was denouncing being in public places where "Vatican II believers...Protestants, Eastern Orthodox, and Jєωs" are present?  If so, he just precluded himself from visiting hospitals, restaurants, airports, or grocery stores.

This is reminiscent of a conference of l'Abbe Pagliarani (FSSPX), in which he criticized the anti-vax movement simply because among anti-vaxers are found some liberals (seemingly implying, therefore, that one should not be anti-vax).  The Novus Ordo Watch seems to be doing the same thing in a different context.

I was not able to find the part in which Msgr. labels these non-Catholics as "children of light, part of the Church, and soldiers in God's army."  Could you quote it for me please?  I am certain that there will be a similar explanation.