I'm not sure where that data is sourced from... Notice it's on the website of a dog food company, who I suspect has an incentive to tell owners that the veg in the dog food is 'natural'.

I suspect if dogs do eat vegetables in the wild, it's only if they can't get enough meat, since their domestication has made them less good hunters. Their wild counterparts, grey wolves, don't seem to ever eat vegetation (except when sick).