I didn't know you could SEND mail with Hide My Email feature, but apparently this is a feature directly in the Mail app. Tapping the From in the mail compose screen opens a dropdown of possible addresses to use or create a new one with Hide My Email.

Hilarious that someone would go to the length of creating 134 anonymized email addresses, but all of them using the same Apple account. Might as well have put in the effort for actual anonymous email addresses.

That was... entirely expected.