If you visit your home (native place) each week on Saturday and come back on Monday to the hostel then in such a case you shall offer qasr salah in the hostel and while in journey after going out of the outskirt of the your city i.e. you shall offer only two rakah of fardh salah that are of four rakahs. Whenever you intend to stay in your hostel for fifteen days or more then you shall not do qasr in the hostel rather you shall offer full salah. If you intend to stay in the hostel for fifteen days first time or more then the ruling is same and if you do it more than once then also the ruling is same. Thus the brother who advised you to offer full salah is not correct.
Allah knows Best!
Darul Uloom Deoband