Adult P. ciliata do not live in cavities in rubble or coral, so I would be very unlikely to find one hitch-hiking. New recruits in the 22-24 mm range will settle out in rubble, so it is possible that you could get a very small one. However, they usually bail as soon as the rock is pulled from the water.
Contrary to the comment above, there are several spearers that do live in cavities in rock, rubble and coral and they could easily show up as a hitch-hiker. In fact, they rarely leave their cavities, so the only way I can catch them is by breaking rubble. The most likely spearers to be found in Indo-Pacific rock are members of the genus Raoulserenea. There are 5 species and all live in cavities and some like R. pygmea which I described from Moorea can be very abundant. In the Caribbean, Meiosquilla lebouri is frequently found in cavities in rubble. There are also several members of the family Coronididae that are spearers that live in cavities in LR.
Roy