A spectrum suggests varying degrees of a single condition, and would be compatible with both the hypothesis that all occurrences of this condition share a cause and the hypothesis of multiple causes. So to claim there are multiple causes is different from saying that cases fall on a spectrum. It tells you that multiple conditions can appear the same way, so they get diagnostically grouped together based on symptoms even though the underlying causes, and so the appropriate treatments, can be quite different.

The 'spectrum' terminology comes about from the field of peychology only being able to attempt to analyze ... basically, 'symptoms', behavioral profiles, phenotypes, and also the field of psychology constantly changing how it does those analyses as well as categorize observable behaviors into conditions/disorders.

What this new understsnding is pointing toward is that there is an actual, identifiable, genomic variance of mutation clusters that actually explains how differences in that spectrum of 'symptoms' actually work, what actually causes which ones.

But now it's a conclusion and presumably a publication that can be referred to.