What's wrong with a Pop Tart?

So I brought my 2yr old daughter to one of her "playdate" friend's birthday party this morning. Since my daughter gets car sick shortly after she wakes up, we usually grab a pack of pop tarts or some waffles that she can eat for breakfast when we get to our destination. So we get there and she wants her pop tarts. As I'm pulling them out of her diaper bag, this other 2yr old little boy (family to the birthday girl, never met them before) tries to snatch them out of my hand. So I pull back and proceed to open. My daughter is a VERY good "sharer" with other children and she knows he wants some. So we offer him some, he gets his little bite size piece and walks away. Shortly after, he's back leaning on my leg wanting another piece, again, I give him another bite size piece and he walks away. Right after that, his father very aggressively approaches me and says (with a raised mean voice) " DON"T give him anymore!" Dumb founded & confused at his tone, I say "OOOkkk, I'm sorry." Then he says again even louder "NO MORE!" then walks away, sits in another room where he can still see me, giving me the stink eye. At the time I was sitting in a circle of three other moms from my daughters playgroup. We all kind of look at each other, I look down at the package and say "It's just a pop tart" with a confused face. First thing I thought of was maybe he didn't want him having sugar, but I seen the little boy eating the sugary snacks provided at the party. Then one of the moms says "Maybe it's not Kosher" and check the package to confirm that it wasn't. I asked her what that meant, but she said she'd have to tell me another time. So I came home and googled it and it seems to involve religion although what I've read involves meat. Let me say, that I have NEVER given a child I didn't know our food without checking with parents first. This was the first time I've ever done it. I guess the fact that he wanted it so badly by trying to take it from me, it just slipped my mind. However I think the guy approached me all wrong and I'm pretty upset about it. I would have never done that to another parent or child knowing that they were only being polite to my child. I would have approached them and said " Thank you for sharing with my son, but that's something we don't allow him to have, so if he comes back for more just let me know so I can handle it"...ya know...something along those lines. So anyway, what was it about a pop tart that set him off so badly? What made him so mad that he treated me that way in front of everyone?