I personally would have waited until the officer arrived to inform him/her that I was carrying. Announcing it in front of the other half of a civil problem is, IMO, begging for them to spout some BS about you pulling it on them. If there aren't other witnesses it just becomes a he said / she said and you run a chance of losing that battle.
There is no duty to inform but I like to be on the safe side. This fall I went with my uncle to get some of his personal items that his ex-wife had....I waited for the officer to arrive before I told him that I was armed.
Hope everything aside from that turned out well.