>>54771157That seems to be the case. According to Khu, Tera form and Tera state aren't the same thing and they can stack, and it fits with the official terminology.
The name for the state of pokemon affected by the terastal phenomenon, is テラスタルした姿 (terastal appearance), while the name of bearded Terapagos's look is テラスタルフォルム (terastal form).
Considering Heath's drawing depicts a Terapagos way more impressive than the one revealed thus far, I would say there are indeed three different Terapagos looks, normal, tera form, and tera form's tera state
