Time and time again it is seen in RF that certain people (especially certain Atheists do) telling other people that their understanding is wrong on their own religious belief, while the person who isn't from their religion actually claim to know their religion and teaching better than the believer....
Why do you believe your understanding is better than the person who actually follow the religion you claim to know so well?
As a polytheist, I've encountered all manner of know-it-alls, both outsiders and those claiming to be polytheists and Pagans. And, in my experience, it's a mixed bag. It's entirely possible for some non-practitioners to know better than someone who claims to be one. I've also seen people who claim a religion who truly don't know jack about their own religion. Though, this can happen in any religion. My favorite was a friend's co-worker, a devout Christian from a Christian background who argued with my friend for saying Jesus was Jewish, she insisted he was a Christian. Technically, my friend was a non-Christian however, she'd also been raised by her devout Christian grandparents so even though she wasn't of the religion, she could go 'round with anyone who was.
I'm sure that kind of thing happens in all religions. I've encountered Pagans who are the equivalent of my friend's co-worker. They can be as bad as the know-it-all, but knows nothing, outsider who thinks their religion's propaganda against your religion is fact and want to insist that you're wrong.