It was written somewhere on iota's official website, CFB is using BCNext as pseudo on Reddit for more than a
year and on nxtslack in #random on 12th July he claimed it directly explaining that he as BCNext had always said that he will leave and as CFB that he was only working under contract. Perhaps slack did not deleted yet, have a look.
This is no proof, I believe there is no proof possible anymore, we all know the genesis passphrase, and when he disapeared BCNext gave CFB, every credentials. Only probability is quite high that it can true.
If true, it is legit that David uses BCNext reputation to sale his soup.
If bullshit, CFB is evil, which is hard to believe.
But everything is possible because CFB knows that if BCNext would dare to react to such an usurpation, he would have no proof to use.