Yes you are correct, technically the 74LS48 is not open collector, however the 2 k pullup is useless to supply drive current to an led display ( very dim, and as far a drive current goes I consider it equivalent to o/c) the use of the sip I mentioned gives sufficient current for a viewable display.
Just for arguement sake, the on chip 2k pullup resistor will give a drive current of : 5v(vcc) -1.6v (assumed display forward voltage)/2000 ohms = 0.00156A or 1.56mA , you see, not much for driving a display. It gets even worse if you use a display with a higher forward voltage such as green ,yellow, or blue.
The use of a 330 ohm sip will render a drive current of about 12 mA.
( assuming a 1.6v display forward voltage and taking the 2k on chip pullup into account ).