I think he'll be fine. Because of the chicken "treat" he may not have eaten as much other food today as he usually does -- thus less poop! If he's not throwing up or having loose stools, he's probably just fine. Just be careful when feeding him meat that it is not too highly seasoned, it could upset his stomach. Ususally plain boiled chicken breast is good. Also, limit these kinds of treats so you can be sure to maintain a healthy weight for your little guy. (Sounds like you need to establish who the real "mommy" is -- grandmom may spoil him!
). My pup loves "healthy" treats like carrots, apples and other fruits -- maybe try him on some of those. Good luck with your new pup!