The explanations provided by others is correct, so I will just confirm that this is indeed correct behavior (and also a rather interesting corner case). When the round ends, the player(s) with the lowest pip count get a point. The bone count doesn't matter, only the pip count does. Typically this comes into play when the round ends because nobody can place a bone, but in this case one player was left with a 0-0 bone, triggering the same rule.

I'll look into clarifying this in the rules, but it is not a bug.