Is it normal that when I call out from a Demo phone it displays a Caller ID from Texas?

Yes, this is normal.

All GreenLink demo phones are temporarily configured as GreenLink test devices and are assigned phone numbers with Texas area codes for testing and provisioning purposes.

Because of this setup, outbound calls made from a demo phone may display a Texas Caller ID until the phone is fully configured and assigned to your company’s phone system and main business number.