Proof would be good but honestly this seems pretty likely.
Not proof of anything related to the blackout and retaliation...
But Reddit absolutely does have an account linking backend they rely on. When my main account was permanently suspended (for quoting what a cop said to me in a private subreddit in a cop thread, was banned for "hateful content.")... they went back through my linked accounts and banned them for whatever reason they could find. Included was one account that used a different email address. Had multiple accounts only because I was using it them to segregate my topics before multireddits existed. One for politics, one for tech news, one for popular subs, etc... The one with the different email address was my politics account and they banned it for visiting a sub I was timed out from by moderators. Over a year prior.
Reddit is completely capable of being thorough (though capricious) in their attempts of policing users.