If that policy is true, I don't have any problem following it. Their range, their rules. BUT the actions of this range officer were, in my view, extreemly unsafe and uncalled for. I am in the process of filing a formal complaint against the man, and have contacted Major hunter of the DNR conservation officers to try and get things moving.
What do YOU think about the situation?
I think you need to very RESPECTFULLY ask for them to cite you the regulation. You may want to print out the regulations and provide them a copy. Doing so will make it very difficult for them to 'fudge' a new regulation that does not exist.
Here is a link to their rules (pdf format): http://www.in.gov/dnr/forestry/files/312IAC8.pdf
FWIW, I did a document search for the term HANDGUN and found no references. I did a document search for the term PISTOL and found 1 reference. I did a document search for the term HOLSTER and found no references. That all said, it would be hard to have a regulation that forbids holstered weapons if they don't use the term holster.