Your guess is as good as mine, but I'd guess that this is just another manifestation of autistic traits being primarily described in terms of how they impact the observer, instead of as an internal experience.
Or another possibility is that they consider social interaction the most relevant aspect, and the other traits are to be considered (or not) only so far as they affect your ability to interact socially.
(which might just be another way to say the same thing)
In other words, they don't specify which traits might lead to a person having "decreased interest in social communication", it might be sensory sensitivities or not, all that matters is if that "decreased interest" is observable.