pretty much true of all Satsuki, even the ones listed as being more apically dominant rather than basally dominant. While I understand what the term means for growth pattern, I have no idea what it means physiologically for the azalea. SO I will just say, most azalea trunks will increase in diameter while in a bonsai pot. Period. I won't generalize beyond that.
Probably one reason is as bonsai there is a tendency to pot azalea in deeper and slightly larger volume pot than maples or elms of similar size. Again not certain if this is causal, but might be a factor.
The deeper and slightly larger pots for the azalea are done for the health of the tree, pot them too shallow and they won't do well. Or so all I've been told seems to say. They are probably exceptions floating around out there.