I don't think this is a loaded question. The attenuation of beers can differ substantially based upon mash temperatures and base ingredients. There are a variety of compounds that can increase the gravity of a wort/beer that are nonetheless unfermentable.
That said, I can't give you a direct answer NTex. I haven't used millet malt myself yet. Experiments using rice malt so far have been confusing; there's a lot going on in a mash, and we just haven't dialed in how all these grains work as well as we have with barley.
The higher mash temp does kinda imply a less-attenuable wort will result. But it could be incomplete conversion too; things like partially-broken down starches adding body but not being fermentable. The rice beers I've been making suffer from similarly low attenuation and I'm suspicious that's the issue. Maybe I should just throw some Beano in a test batch to see if it ferments all the way down or not.
Have you tried adding enzymes? That would let you know if those extra gravity points are from incomplete conversion or not.
But more crucially, does it taste balanced? If it's not too sweet/syrupy then you're probably gonna be fine, you'll just have a lower ABV and a kinda starchy beer. And cloudiness is no issue with a witbeer.