Maybe I was just not prepared enough for my conversation with the head of engineering. Still though, I would love to know why.
Thank you for your advice, I feel that's really all I can do. Still, it's hard to not let this get to me.
Don't let it bother you and just think of it as another story to tell[1]. If the no-reply bothers you, then they probably have a lot of other habits in how they treat people that would really bother you if you had got the job. Its the canary in the mine. Don't think of it as getting rejected, think of it as dodging a bullet.
1) my most wtf? story is getting rejected for an internship because the area code of the high school and college I went to was the same. Told me that over the phone. I did at least point out the whole state is one area code.
I have not had something like this happen to me, but I am sure it will get easier after another round of interviews with another company. You will almost forget about this experience after you land a good opportunity, other than for the anecdotal value :-)