In other words, the excuse was that ads embedded on firearms channels might give their customers the "wrong impression" about those companies and their products, and Google didn't want to anger their advertising partners. 

It's hard to say how accurate this claim was. The exposure of ESG and Big Tech collusion with government agencies to censor conservative platforms supports the idea that there was probably an organized corporate push to suppress the political opposition on YouTube as much as there was an effort to shut them down on social media.

The majority of conservative content creators understood that this was not about advertisers, it was about narratives.  The exploding popularity of gun channels runs contrary to the media assertion that American society is moving increasingly to the left.  And, even though gun channels mostly focus on firearms and instruction, they also promoted conservative and constitutional values which represent a thorn in the side of the establishment.

More proof has surfaced that randomized advertising and company complaints were never the issue.  Gun related channels are reporting that Google/YouTube is not only demonetizing them, they are also no longer allowed to feature private sponsors that market gun related products.