I love how the assumption is that the problem is with the interviewee rather than the startup - so confident of this, in fact, that they feel obliged to write a blog post asserting this.
Defensive anyone?
Notice the assumption here, that their 20-minute task is a perfectly reliable indicator of how the interviewee would behave in general.
The interviewee was right to leave them without saying a word.
God I get sick of the smugness. You can cut it with a knife.