The text mode on that TV is for the closed caption text that can be used for viewing simple text data such as a weather report. The teletext broadcast by WTBS was a much more advanced interactive system similar to what's used in Europe.
http://en.wikipedia.org/wiki/Teletext
Zenith did make some sets that could receive this signal, but it never became popular.
The "Sentry 2" name is meaningless. It's just a name to sound a little less than the higher end "System 3" models.