Face gesture somehow working on iPad 9 (which does not have a TrueDepth camera)?

FaceID or the TrueDepth camera is a prerequisite for gesture page turning as per https://help.piascore.com/hc/en-us/articles/360000986152-I-can-t-find-gesture-page-turning-smile-icon . However, somehow this feature works on my iPad 9 (base model) which does not have FaceID (only TouchID). Was this feature added for non FaceID devices later? If so, I could contact the providers of music score readers to implement this feature as well. 

If FaceID is not required for gesture page turning, one could get the much cheaper iPad Air 13".