I could be wrong, but if it was candida in my mouth, wouldn't the thrush be all over my mouth? I spent some time looking at pics online today and almost everyone that had thrush had it all over their mouth, not just their tongue. I have nothing but pink everywhere in my mouth, except for this patch of white right in the middle and outer edges of my tongue.
Here's the weird thing though about the candida, I don't have any symptoms of it other than my tongue. And when I took the stool test I had already been off the strict strict candida diet for a month. I have been eating about 120-150 grams of carbs a day from things like quinoa, sweet potatoes, brown rice pasta without any issue. I know some people eat those items on their candida diet, but I was incredibly strict and just stuck to meat/veggies for 4 months.
Interesting that you mentioned Biotene as I found a bottle of it unopened at my mom's house and started using it a couple nights ago. I'll use it and take note of how my tongue looks shortly before and and after.
If I do have a candida issue, would a probiotic help get rid of the tongue coating? If I have some type of dysbiosis (which I believe I do) wouldn't re-populating the environment do the trick?