You're right that absent some colossal screwup you could never prove one way or another that it was legit vs planted, but stuff like that changes my priors on what I believe can happen. The fact that it is completely deniable also increases the incentive for the government to do it, and they no doubt have the capability. Capability and motive combined leads me to believe that it likely does happen.

Oh definitely. I'm not saying that it doesn't happen, just that this time I don't think that's the case here