I would email UIL a copy of the solo and ask about it. Many of the other ensemble codes have "any published instrumentation may be performed" following them. If the score has a mixed instrumentation then it seems the PML has it miscategorized in 234 instead of 230.

It took me a bit to find those extra rules years ago - I hate how they are buried in the PML page under a separate tab instead of listed on a page on the UIL music site like the marching/concert/sightreading rules and requirements.