So confused about pizza cals!

So today I ate at the hospital cafeteria. The pizza slices were all the same size but had vastly different calorie amounts.
Example:

Ham and pineapple: 640 cal
Cheese: 420
Chicken and Spinach: 260
Veggie: 460

Does that make any sense? I especially don't understand why chicken and spinach was so much lower than the veggie! Looked like the same amount of cheese and crust to me. Does that make sense to you, or do you think the hospital measured the cals wrong?

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