How do evolution stones work? In the games, pokemon can hold the evo stones without evolving, but in the anime, they automatically evolve when they touch it, even if it's unintentional. How does that work?
It’s possible that the concept of a Pokemon ‘holding’ an item doesn’t necessarily mean it comes into contact with the Pokemon. After all, if a Pokemon needs all of it’s limbs to battle, it can’t be occupied holding a berry.
Consider mega stones: while it’s safe to assume the stone is touching the Pokemon in order for it to evolve, the same concept can be applied to other items: little satchels or holders that the Pokemon can access to eat the berry or access a held item.
The only practical reason I can see for a Pokemon to be given an evolutionary stone to ‘hold’ anyways is to trade, in which case they could be held in a bag or stored separately in the Poke ball they are in
That would go against the trading evolution mechanic where you evolve, say, an Onix by having it hold a steel coat, but the way I always thought of trade items working is that the item is combined with the Pokemon’s code in the Poke ball during trading, while evolutionary stones work with the radiation of the stone. Touching one while it’s digital/energy cannot trigger evolution.