Did I store these potatoes incorrectly (found a bug inside)?
Potatoes and the plants foliage are a feast for a lot of insects, some good some not so good, but as far as I'm aware none that will do you any harm. As bmargulies said, don't worry overly about it.

If you're 'really' interested, you can take a look at this site, see if you can spot your 'badguy' :)

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