M4 Engineering interview questions

Went in a for 1 hour interview, spoke with an R&D specialist and asked general get-to-know you questions. That went on for about 30 minutes. Then waited for a presentation portion. Meanwhile, I sat with the Co-Founder and showed him some experience. He seemed interested and I did enjoy our casual conversation. Then, went for the final assignment and was asked a few Linux CMD questions, aircraft dynamics, and math interpolation question. Of everything, I was hammered on how I did the linear interpolation. Apologies for forgetting the equation name but they dismissed the fact I derived the equation and solved appropriately. I spent 45 extra minutes explaining my derivation, and they seemed disappointed that I couldn't remember the equation name: point-slope form?

In person Interview.30 min basic interview questions and 30 min technical interview with one coding question and one aerodynamics question. The coding question was to write a code which does interpolation in any language of preference.