You sure it was not a second "first officer?"
Positive. Although obviously it could have been a slip of the tongue on the part of the announcer. I like to think I have a basic understanding of the different people who operate airplanes (you'll notice there was no reference to co-pilots in the OP) but this one threw me off.
check captain "checker" on board.
Would something like that typically be announced to the passengers? I wouldn't have thought so based on the possibility it could be misunderstood by nervous/inexperienced flyers. ie "What do you mean the captain's in training!!!"
Michael