You are right. Interviewers generally ask about backpropagation. They should definitely test me on neural network concepts. But do you not think, asking to code entire neural network from scratch was an overdo for the interview?

It's definitely an easy question if it was a common question and hence featured on leetcode, where candidates would practice it before the interview.

Someone with 2 years of experience don't remember the knitty gritty maths to implement NN from scratch. This question is more suited for someone fresh out of college, in my opinion.

Everything. Loss function, optimizer, backpropagation, update weights