I will be interested to see if he returns.
I suspect that he means:
"My friend looked at his transaction history on IR to see where the bitcoins were sent to."
Not:
"My friend got an address from IR and then used that address to send the bitcoins to me."
When you asked "Where did your friend obtain the 1NxR3TLr1AXYYodX7EC2PVYqWL1XuQcC8m address", I think the OP didn't realize that you meant:
"How did your friend choose an address to send the bitcoins to?"
And instead accidentally thought that you meant:
"How did you determine that the address 1NxR3TLr1AXYYodX7EC2PVYqWL1XuQcC8m was the one you had used?"
These are possibilities, but I suspect that the more likely scenario is a mis-communiation between yourself and OP.
Yes. The important question that ONLY the OP and his friend can answer is:
"What was communicated when you were getting ready to send the transaction, and where did that information come from?"
I doubt that they are.