Nope, that's not how Twilio works. Yes, someone else sent a spam message, but Twilio did not forward it to "their customer's list" whatever that means. Twilio forwarded it to their customer's application, which was the end of the line for Twilio. At that point, their customer's application sent out that spam message to whoever was configured to receive it. As far as Twilio is concerned, the incoming and outgoing messages have no relation.