I can't really judge, but by the sounds of it the paper didn't provide enough evidence to prove that it was true, or at least didn't make it obvious that it was true. They even admit that the data presented was "suggestive" that it might be true.

This is something you see all the time. Someone does a limited experiment, gets the result they where hoping for, and then get super excited and carried away and claim that their entire thesis has been proven true. I've rejected (or rather sent back for extensive revision) papers myself based on this, even when my gut feeling was that their conclusion was probably correct. Often the paper comes back with a more moderated conclusion and then gets published without a problem.