Why appears this: This email was sent to mdmleyton@gmail.com in an email alert?

Like Robb pointed out, this information is derived from the default footer when you forget to include the appropriate "unsubscribe" link in non-operational emails.  The question I have - and this will determine if this person received the email as well - is did you use a "send email" or "send alert" flow step?  If you used the "send email" flow step, this was sent to the lead.  If you used the "send alert" flow step, you probably just forgot to indicate that this was an operational email in your alert email.

Please mark the response as Correct Answer.  Thanks!