Unlike another signalgate post here that misused Occam's Razor, this is the most parsimonious explanation. The other post was arguing a more complicated, not less complicated scenario

Moreover and most likely comporting with the truth that Waltz is avoiding, Goldberg’s contact information was in Waltz’s phone because Waltz put it there just like he included Goldberg in the Signal group

I disagree with this part though

The lens of Occam’s razor tells us that Goldberg is right, Waltz is lying and that makes Waltz a compromised insider threat to Trump’s Administration

I don't see him as a compromised Insider threat. I don't think he deliberately added Goldberg. I think he simply screwed up.

I also think that's the Occam's razor explanation.