Because it can and it was your lucky day.

The tollerances on modern RS232 interfaces are very wide... and the PIC is resilient. With your PIC parked next to your PC with a few feet of cable yes it'll probably work - but there are no guarantees.

RS-232 is capable of being driven to 1km without Line Boosters... there is no way your PIC will connect directly at that distance - or even one-fifth of that distance.

Try connecting to an old Tandy TRS-80, Superbrain, Zenith Z-89 or DEC PDP-8 and tell us if it works...