Are we interpreting OP differently? From all I can read of available information, they seem to have been reasonable. Sounds more like their neighbor or the previous tenant had a meth lab.
Parent commenter's account was compromised.
Are you assuming its SendGrid's fault the account was compromised? I'd assume the opposite.
Stretching the analogy, it's more like OP had the room keys lying on a table at a cafe, someone managed to copy the key after sniping a photo and then abused the room while OP was out for the night, and then OP notified the hotel staff once they got back and realized what was going on.
In both cases, OP was unaware of anyone having unauthorized access and it wouldn't have happened (as easily( if the business had better security.