I'm quite frustrated they are calling this end to end. I can't find it now but a tweet earlier indicated that they have the keys and can help law enforcement with investigations which means it's can't be end to end.
AB/BC link encryption is the correct way to refer to such a scheme.
"Unlike PGP and S/MIME, STARTTLS provides hop-to-hop encryption (TLS for email), not end-to-end."
[0] https://www.eff.org/deeplinks/2018/06/technical-deep-dive-st...