The meeting was either on May 10th or May 6th 2016 - Downer’s diary says May 10th, and he and Papadopoulous both gave that date, but the Mueller report says May 6th. I think the May 10th date is probably correct (I wonder if May 6th is when Papadopolous met Erika Thompson), but either way, by May 3rd 2016, Trump wasn’t just a nominee, he was considered the presumptive nominee after his victory in the Indiana Primary and the withdrawal of Ted Cruz and John Kasich. Downer is correctly quoted in saying he was still just a candidate and hadn’t won the nomination, but do you honestly believe he didn’t know that Trump was already well ahead of any other Republican candidate?
I have no idea what Downer knew at the time but he was saying it specifically to downplay the significance of it. That severely undercuts your efforts to make it a significant fact.