Request from buyer after Kijiji sale

I sold a dumbbell (new in sealed box) to a guy after posting it on Kijiji.

Everything went smoothly during pick up - he paid the amount agreed on with cash. A few minutes later, he sent me the following text,

"Hey thanks again. Everything looks good. Can you please confirm the details of our transaction if you have a second. It is just so I have a record and can expense it at work (replying confirmed is good enough):

Ad ID _________

Settled in cash on Dec 31, 2020"

Just wondering before I go ahead and "confirm" that it is safe for me to do so and won't backfire on me in any way. The guy seemed nice enough and I would like to help him out if I can as long as I'm not putting myself at risk here. Is there anything I need to be aware of before going ahead and confirming this sale through replying to his text?

The guy did seem a little nervous (not overly though) and I encouraged him to go ahead and open the box to check the dumbbell but he didn't seem too concerned and eventually did not inspect the dumbbell like I would have expected. Am I reading too much into this ?