Are fresh, raw cashews different from store-bought?
Nuts can go rancid. I've also had stale nuts, pecans or peanuts that were exposed to too much humidity. This adversely affects the texture. They need to be fresher than that.

Cashews, however, are in a slightly different boat. See Anacardium occidentale L.

Cashews have a toxin in their shells that resembles poison ivy. When harvested, cashews are roasted in their shells to reduce the toxin and make the shells brittle and easy to remove.

If these cashews were harvested by an amateur this process might have not been done correctly and you may be reacting to the toxin.