Hasn't Stinkachu legally become the pet of different characters like Heatstroke and Foghorn in separate alternate realities? It's completely normal to give your pet a name, whatever it thought to call itself is of no consequence. I'd imagine Volt got himself in trouble again and the final outcome was him becoming someone else's property, after taking him to the vet to get tested, registered and chipped his new name became Stinkachu.