got reject in nagarro

I had a rapid-fire interview round at Nagarro that lasted approximately 20 minutes. The questions spanned various technical areas, including core programming concepts like polymorphism, data structures (stacks, queues, graphs, trees, linked lists), database concepts (joins, ACID properties), and algorithms (BFS, DFS, 'implement stack using queue', 'reverse LL', 'frog jump puzzle'). While I felt confident in most of my answers, I admit to mixing up balanced binary trees with complete binary trees and struggling with a specific part of the joins question. Throughout the interview, I had the impression the interviewer wasn't fully attentive, as I frequently had to confirm his presence. Despite this, he provided positive feedback, stating the interview was good. However, two days later, I received an email from HR informing me that I had not cleared the round, which came as a surprise given the initial feedback.