This is the 15945th most frequent Russian word.
проучиться
To study for a certain period.
In this sentence, the word "проучился" means that the subject completed a period of study, indicating a process of education lasting four years, and implies completion of that period.
Я проучился в университете четыре года.
I studied in the university for four years.
Here, "проучиться" is used to describe the decision to extend studying over a defined period in the future, implying temporary continuation.
Она решила проучиться в колледже ещё один семестр.
She decided to study in college for one more semester.
This usage of "проучились" conveys the idea of sharing a study period over time, reflecting the continuity and completion of joint educational experiences.