There's absolutely nothing to be confused! 

The answer lies in the most important document of all - the sale and purchase agreement. Have you taken the time to read it? 

At the back of the agreement, there ought to be a Schedule. At the bottom of the schedule there will be a clause like this:

Within twenty-one (21) working days after receipt by
the Purchaser or the Purchaser’s solicitors of the
separate document of title to the said Lot together with a
valid and registrable Memorandum of Transfer to the
Purchaser duly executed by the Vendor or on the date
the Purchaser takes vacant possession of the said
Building, whichever is later.              2.5 %

On the date the Purchaser takes vacant possession of the
said Building as in item 3 and to be held by the Vendor's
solicitor as stakeholder for payment to the Vendor as
follows:-
(a) two point five per centum (2.5%) at the expiry
of six (6) months after the date the Purchaser
takes vacant possession of the said Building;
(b) two point five per centum (2.5%) at the expiry
of eighteen (18) months after the date the
Purchaser takes vacant possession of the said
Building.
There you go. 

No. It's still residential, isn't it? 

Hostel in the business sense would mean like YMCA - a basic hostel for rent on a daily basis. That means there is a signboard placed on the building and the whole building is officially referred to as a hostel and is run in that sense.

If it is merely a case of multiple units being rented out to students, thus giving it an appearance as a student hostel due to the large number of student occupants, it will not be considered as a business. Thus, there would be no case of complaint against the developer/owner of the units.

Hope that clarifies things accordingly.