What sorts of nuts were you giving them? Still in their shells or not? And not salted or flavoured I hope!

Something like peanuts (not a nut at all but that's for another day) can be bad for them as can pistachios and some others can be very harmful. Any left on the ground can rot or attract rats and pigeons and they create other problems for the park.

Squirrels do like nuts but they have to eat other food too like fruit and vegetables to have a balanced diet or like humans they get fat!

There are notices on all the main gates with the park rules on and I'm sure it says there not to feed them (or the pigeons) but in the uk we tend not to have masses of notices all over the place in parks so that's why you probably didn't see any.

If the park emoloyee was polite - I assume it was someone official and not just another visitor ( though as you say '1 guy' so it more likely could be another visitor) I see no reason to complain as seems the suggestion earlier in. It's their job to look after the park and the animals and to make sure it's there for years to come and enjoy.