And the article says thus: It had become Johnston’s job to travel all over the U.S. to show off the Dash 80, as the 707 was code-named.
Dash 80 was a nickname for that particular plane, it's model number is 367-80. The 707 is a slightly different aircraft that generally isn't referred to as a "Dash 80".
The Dash 80 was the prototype for the 707, but strictly speaking, it's model number isn't 707.