Yes, in a year there are 52 weeks. However, you can usually ask the interviewer if you can simplify things and use 50, in particular if you are doing market sizing/estimation.
It seems PrepLounge reported directly the approximated value. Same thing for the number of days in 3 years for which they reported 1000 instead of 1095.
It is important you explicitly ask the interviewer if you can approximate, as otherwise he/she may assume you made a mistake / don’t know the real value.