doesnt matter if he wasnt just walking this dog! its a stupid answer! Could have been working fox, pest control, rats anything!
Your dog will have to toughen up mate, if you want it to do bushing work, it will come accross alot worse things than nettles... they dont hurt half as much as barbed wire!
a dog will never toughen up to nettle stings it just like saying a human will. its hurts as much the first time as it does the last, they just have to deal with it my terreir deals with it till i get him home then he will run all over the house, spinning on his back itching his self its