I'm with Timbers on this one.
You guys seem to forget that if you can see riders going a certain way up ahead, you tend to follow them. But when you're on your own and can't see any, and you miss an arrow, you don't know that you've missed an arrow. When you're riding head down, it's easy to do - I did it at the '07 Golden Triangle Epic and at the '08 GMBC Long Loop (in fact at that one I rode straight through bunting the wrong way as I had my head down and was towing a train of about 8 riders - the first 4 of which followed me straight through the bunting), and a whole bunch of riders did it at the '08 Golden Triangle Epic which took them 10km off course.
Unfortunately this event isn't an MTBA one, but from memory the MTBA requirements for marathons is that any intersections must have at least two markings indicating a turn coming up, with a different marking for the final arrow. Some events even go as far as to put an X after any possible wrong turns, and a marking after correct turns. Bunting across any wrong turns is also helpful.
Part of the pre-ride checks for the course should include the fact that all markings are well and truly clear and visible. Running an event comes with the responsibility to do it right, and he's well and truly entitled to point out where things need improvement.
Edit: Also, officials being smart-asses isn't on.