"Huh?" The prince tilted his head as he felt puzzled as to why the girl deliberately gave him a full description of the cake.
She acts as if she is like a pestering saleswoman, trying her best to convince him (customer) to buy a cake from her store.
[Does she really think by telling me how great that cake is would actually get me to celebrate my birthday? Sometimes I wonder what really goes on in that head of hers.]
After that, she just sighed and said, "Okay. Then I'll just have it by myself this year again."
"Huh? Why? I thought that cake was meant for me?"
"Well, your highness didn't want it, and I can't throw it away. It's a LIMITED EDITION. It would just be a waste, and if your highness is not going to celebrate your birthday, then I'll just enjoy it on your highness behalf then."
[what?] he thought as he tilted his head [what is this strange girl saying?]