Tomato Sauce is not Tomato Ketchup??

Scene:
I requested helper to heat up the fries and asked for tomato sauce.

Me: Auntie, you forgot to give me tomato sauce.
Helper: Sachet one can?
Me: Okay.

A good two minutes or so later…

Me: Auntie, cannot find tomato sauce?
Helper: Ya, don’t have tomato sauce already. Tomato ketchup can?

My father who listened in to this conversation started laughing and shook his head.

Me: Auntie, please tell me the difference between tomato sauce and tomato ketchup? Aren’t they the same? You mean you don’t know?
Helper: *laughs and thinks it’s funny*

Question:
Was my request a tall order or what?! I don’t know lah… Enlighten me, please… the difference between tomato sauce and tomato ketchup??!