I was more commenting on the uses of xanthum gum to be helpful, but reading through the Nova classifications... They seem problematic in the exact way you're describing here and are at best a proxy for nutrition that can be manipulated, using words like "simple food products" and "rare culinary use" is ripe for interpretation.

The bill itself calls out using USDA databases for various ingredients and various sections of federal regulations, so I can't comment too much about how they'd feel about xanthum gum without diving deep. Not to go off on a tangent, but just from the bill's text, I can say for sure they don't like nonnutritive sweeteners, which I think really hurts diabetics choices at reducing their reliance on insulin while still enjoying nice treats. Although not too important for a school meal, it's definitely part of the ultra processed conversation and why it's not a simple thing to categorize food into groups.