When that happens on clay flower pots, it's salts leaching from the soil and water in the pot. If your bowl has hairline cracks (many old crockery pieces have 'crazed' areas), it could have absorbed salts from the contents. Or, if put in a DW, could have absorbed salts from DW detergent.

I'd soak it in a basin of plain water, wipe, and let dry thoroughly.

This may sound totally out of whack, but tell me this: if you run your finger over that stuff, does it come off easily and does it have webby/fuzzy stuff between the larger white pieces? That looks more to me like an infestation of meal moths. Was this bowl stored in a pantry where flour/bread/crackers and such were stored? Maybe something left in a bowl that was underneath this bowl?

Its just a bowl in a stack of bowls stored with the pyrex and glass cookwear. No bugs anywhere round...and it is only that bowl...it does have some crazing in the glaze so perhaps it is the salt.