Nothing, really. This is just the top row of keys on an English-language keyboard. Tomlinson was just testing out the system and using a nonsense message. He had no concept that he was going to start a revolution in communication.
Tomlinson was one of a group of scientists who were working on developing better computers.The scientists at his site were able to send a message to a "mailbox" on the computer on their site. Other scientists could view the messages in the mailbox. But there were other computers at other sites where scientists were working on the same project. Tomlinson's idea was to figure out a way to deliver messages to mailboxes on those remote computers. He used the @ sign to identify messages that were headed out of the local machine to the more distant ones. That was the start of the emailing systems that we still use today.
At first, the number of people on email was small, but by the end of the 20th century, there were 263 million email boxes. In the 21st century, that figure has grow to over 2 billion, and the functions of email services in the future will become more and more diversified.And text messaging on cell phones is also increasing so people can, in effect, be in constant touch with people who are long distances away.