Incoming text message auto filled the "TO" field?
This spammer must have acquired these contact numbers from an email account's contacts page belonging to one of the people who received this. Then, they sent a text message to some of the contacts they found. The To field is auto-filled by your phone with all the people who received the text. For instance, if I texted a message to you and some guy (let's call him Joe Smith) the To field would be filled with "To John Ramos and Joe Smith", indicating that any text you send in that group chat will go to the people in said group chat; that's exactly what's going on here.