Piggy's exact reaction is best stated in Golding's very own words:
He was intimidated by this uniformed superiority and the offhand authority in Merridew’s voice. He shrank to the other side of Ralph and busied himself with his glasses.
This is certainly a foreshadowing moment because when an author introduces us to a character even if it is through the action of other characters, that speaks loudly of the initial character's persona. Piggy's intimidation of Jack will likely be a recurring theme. Piggy persisted though with Ralph and Jack and made effort at that first meeting to at least assert that stock of who was on the island should be taken into consideration. Jack works a jab at Piggy's appearance through this process and Piggy is further mortified by Jack.