I totally agree with your assessment - it is most likely instance of labeling a set of behaviors without looking at the cause. Many diagnosed with PDA syndrome share similar characteristics of those diagnosed with PANDAS - high anxiety, school refusal, PDD-NOS. Is PDA syndrome really describing a manifestation of auto immune disorder? I would say very possibly.
Truthfully, to me, the value is not in the label of PDA syndrome but rather in the strategies that have been identified to help those with the presentation similar to PANDAS - namely the high anxiety and school refusal. Because not only do we battle in treating the auto immune disorder, we battle with its presentation. And to me, the latter is actually the harder of the two battles.
It is already tough to deal with the high anxiety/school refusal, but it is even worse when the prescribed strategies don't seem to work AT ALL. But what they have determined with PDA syndrome is that normal strategies DO NOT WORK FOR THIS KIDS. To me, this is huge! This so correlates with our experience! So now we might have some better ways to deal with the presentations! Some insight on to what is really going on and HOW TO DEAL WITH IT! In the UK, where the PDA syndrome diagnosis is widely accepted, there are actually schools to deal solely with children with PDA. (But on the flip side, these kids may never get the real help for the root cause of their issues).
I am currently reading Understanding Pathological Demand Avoidance Syndrome in Children by Phil Christie, et al.
Anyway, I just thought I would share . . sorry about the weird spaces and punctuations but I am doing this without my glasses on, which really isn't the best idea.