It is external RC.
I don't have an 18 pin board to refer to, but I do have a 44 pin one.
The 44 pin demo board has a TQFP 16F887 PIC on board. As standard, the OSC pins, RA6/OSC2/CLKOUT (pin31) & RA7/OSC1/CLKIN (pin30), section of the board remain unpopulated. You can use INTOSC without adding anything, or add components (R/C, crystal & caps, or resonator) to use RC LP XT HS etc.
See attached image.
Again, without having a board to hand, I could speculate that the 18 pin board's clock section is probably unpopulated as standard, since the bundled 16F648A has INTOSC...hope someone who has one could chip in & confirm.
Regards.