I just scanned the Harris interview in question. Here it is if you want to watch it:
https://www.youtube.com/watch?v=vEu8hSGDKJA
I don't know what people were expecting. Harris seems like a sane person answering questions about her background and what she'd do as president.
Maybe I'm missing a key part, but I don't know how you can look at that and say she's incompetent or not fit for the job.