@saxnot Not wrong, but in this specific case I suspect that this happened because the file size was above their limit of 25MB. In this case Google stores the file in Google Drive and attaches a link to the email.
https://support.google.com/mail/answer/6584?co=GENIE.Platform%3DDesktop&hl=en
Did a little test with my olf Gmail account and when sending a file with around 7MB, the file was sent directly to my other account.