Refusing one type of food offering but accepting another?

I have a baby ball. 148g about 17 inches long. I have had him for two weeks and he eats every Saturday afternoon. The reptile 'expert' at the pet store told me he had eaten one frozen pinky mouse each of the two Saturdays he had been there. This week when I offered him a pinky he was more interested in eating my thumb rather than the mouse. (I use feeding tongs) Being that the pinky mice were really a little too small a meal for him and I only had two left I had purchased some fuzzies for next week's feeding... He immediately struck and ate the fuzzy when it was offered. Is it normal for him to refuse the pinky even though that is all he has ever eaten? If it matters at all I was just given a 6 month old ball (425 g 34 inches long) 5 days earlier who is eating one medium adult mouse per week. (Also on Saturdays)

The pinky mouse is way to small for him as well are the fuzzies. Fresh out of the egg starts on hoppers.

I generally offer mouse hoppers out of the egg. Most all hatchlings will take a mouse hopper (they like the movement?).

I have found that about 25% of the time a hatchling will take a rat pinky right out of the egg, but generally a mouse hopper is a no brainer. After a few meals I will place a rat pinky/fuzzy in some dirty mouse bedding for 30 minutes and they will take it, making the transition to rats much easier.

I will get some Hoppers and feed those to him. But still why is he refusing the pinky mice? He was obviously hungry and they have been his only food source up until now.

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I will try this. Thank you so much.