The puffer probabley isn't spitting out the squid because it doesn't like them. rather the portion sizes fed are too large. Cut the squid into smaller pieces and feed the puffer a little at a time. Vary the food types as well, in shell shrimp, clam meat, scallop and mussels. Be sure not to feed live/fresh though. Freeze anything you purchase for a few weeks to kill any parasite possibilities. Feed animals in the shell as well to help keep the teeth filed down so they do not overgrow the mouth.
RE: goldfish, it's not that you should feed them only goldfish, it's really that you should never feed them goldfish. It will lead to a host of internal ailments and poor health.
Cheers
Steve