In this case the emotional outburst suggested the founder might be in such close contact with the problem that he might find better solutions, and will likely recognize many non-solutions before wasting time on them.
At least that is a takeaway I would have.
It is not everything a VC might want to hear, but it is a positive.
You can spend so much time on something, yet it wouldn't tell a YC interviewer that it's a problem you're intent to solve.
Case in point, my YC idea. I spent loads of my free time on building a MVP, got praise for it, but I did not have a burning passion to solve that problem, or even any desire that I wanted to be in that space long term.
At least that is a takeaway I would have.
It is not everything a VC might want to hear, but it is a positive.