Not too surprising when you consider there isn't really a standardized guideline and every interviewer asks questions of varying difficulty. Sometimes interviewers don't even ask candidates the same question and tailor them based on the candidate's resume and experiences. I've had interviews as simple as writing a function that outputs if two strings are anagrams, and other interviews that test dynamic programming knowledge and other interviews that tested my knowledge of concurrency. At the end of the day, its luck of the draw which interviewer you get and what questions he decides to ask you.
