Agoda interview questions

I applied online, I got an email of interview with Development manager and another one, The interview was so friendly but they asked me most of questions about front end roles however I applied as Backend developer, he did not ask me anything related to backend, c#, oop, dband sql, or data structure. at the final 30 minutes he gave me one problem solving (see if two sub sets with same number of items are similar or not. I gave him the solution and was working 100% and Time of complexity was O(n) he told me there is a better way and my solution is not good at performance (he did not test it) his solution was 100% wrong !! but i didn't notice during the interview he said we can check the Sum for two sets if equal then they are similar, otherwise not. this will work if the sub set for example {1,2,4}//{4,1,2}. but what if they are {9,6}and {8,7} his solution will fail. then I got a rejection mail from Agoda. I want to say to Agoda, The rejection not from you it's from me.