Piast was the name of Poland's founding dynasty. The term Piast was used to mean an ly native Polish candidate to the throne as opposed to a foreigner.
Piaścik is the diminutive form which possibly meant princeling. Or a toponymic nickname for someone from Piastów or Piastowo.
There are probbaly more nobles with -ski ending surnames, but that does not mean that all -skis were well-born. Often it was a simple toponymic, ie Piastowski (from Piastów), Sokołowski (from Sokłów), etc. with no class implications.
Bukowski is a case in point. Buk is a beech-tree so Bukowo or Buków would be translatable as Beechville, Beechton, Beechshire, Beechwood, etc. and Bukowski would be a toponymic nickname for a local inhabitant thereof.
Krzykalski is from krzyk (shout, scream, cry) -- the perfect nickname for someone wont to get into arguments, raise a fuss, engage in shouting matches, etc. Or a toponymic nickname for someone from Krzykały (Screamton, Rumpusville, Shoutburg).
