The genetic component is well established, though we haven't identified it yet.  The problem with the above results is in the interpretation.  You can't say anything about cause, effect, or even biological linkage.  It's just a difficult to interpret clue.  Progress usually results from a chain of such clues, so each one is a real step forward.  

This study might suggest the diseases are linked, but it might simply mean that normal variation in brain development makes a difference for "borderline" cases, and each variation will affect a different group of diseases.  For example, some people may be a little stronger or weaker in brain region "A".  If two people inherited the same predisposition toward autism, it might only be the weak "A"s who tip into clinical autism.  That same region of the brain might also alter the odds of developing schizophrenia in the presence of other factors.  Yet it doesn't really say that autism and schizophrenia share a cause.