All RVs, regardless of brand, eventually have an issue with the tank sensors reading wrong. Just assume someone used the toilet (shop workers or even contractors the RV dealer hired have been known to use a lot RVs facilities). Sometimes the drive away driver that delivered the RV to the dealer used it. OR, it's just reading wrong.
Anyway, it's a common issue so try to get the tank filled with water soon. Drive around and let it slosh with a small amount of Dawn liquid. When you dump, record the date. Then from then on, always leave the valves closed for the number of days you figure out it takes to almost fill the tanks. Dump, and record the date. Then just empty whenever you go that many days. All this while you're traveling of course.
If it's going to be sitting in storage for weeks or months, always dump the tanks first, then add a few gallons back in so the dump seals are kept wet.