Not necessarily. It's just that Pfizer vaccine has been studied much more extensively in terms of waning protection with most of the data coming out from Israel.

Another factor is the time between two vaccine doses. Some countries were following trial protocol strictly (ie, second dose 3 weeks after the first one for Pfizer). But in many places other places the gap between two doses was much longer (because the vaccines were not readily available so they were "stretching" them out by vaccinating everybody with the first dose first).

I don't think these things have been well studied.