On
Djurens Rätt's website, they say the survey was carried out on subjects from 15 years old and up. So presumably younger children are excluded from the survey, and therefore I don't think they can claim 10% of the entire population is vegetarian.
I do think Sweden is one of the more veggie-friendly countries in Europe, together with the UK and Germany. When I lived in Norway, I knew of fellow veggies who went on trips across the border to buy vegan specialty products. And I myself bought mail-order vegan shoes from Sweden.