It's crazy because it's not default bw behavior, or even any bw behavior... I don't use the cli, but I don't see any built-in capacity to copy bw output to the clipboard. (In the UNIX way, you'd normally pipe it to a clipboard utility if you wanted it copied, and then the security consequences are on you.)

They probably caused it themselves, somehow, and then blamed bitwarden. Note in the original comment they aren't even entirely sure what the command was, and they weren't familiar with it or they wouldn't have been surprised by its output... so how can they be sure what else they did between that command and the weechat thing?

If the terminal or tmux fed terminal history into weechat, that's also not bw's problem.