This is the new warning that was implemented in response to all that drama and handwringing about iframe “vulnerabilities” last month.
Basically, the login form for plus.espn.com is actually an iframe that is displaying a login form hosted on cdn.registerdisney.go.com. Bitwarden is warning you about this, and giving you an opportunity to avoid sending your espn.com login credentials to the go.com site.
It would be nice if there was some Bitwarden branding added to the pop-up warning, though.