When a potato is eaten, the amylase in the saliva mixes with the potato starch and starts breaking it down into sugars, some wil be glucose acording to [1].

You can test this yourself by eating a plain cracker. A plain cracker doesn't contain any sugar, but if you keep chewing it you will notice a sweet taste in the mouth. This is from the sugars released by amylase.

There is no mention of fructose on the amylase wikipedia page. So maybe you are right.

[1] - https://en.wikipedia.org/wiki/Amylase