I suspect the e-mail generated was from his e-mail contact list. Technically it is not spam because it is asking you join. Today there are companies etc that do e-mail farming. They get paid when you open an e-mail generated by the sender.
Not saying this is exactly that. But I think whomever has sent doc e-mails in the past have been picked up and placed into a data bank where AI just generates a generic email with your first name in it...