No it has nothing to do with that... 99% of the world views the metroplex as Dallas. Im not sure there is anyone educated that would think when you say Dallas you were talking only about Dallas, and not the whole metroplex. The issue is that Ft Worth is incredibly insecure about being insignificant compared to Dallas.
The reality is Plano is now the US Headquarters of Toyota (along with YUM, and a dozen other major international companies), but I would be shocked that if they say anything other that "Dallas" in normal correspondence.