I would message them that the mutual cancellation is coming and explain that they need to click on the AGREE link to finalise the transaction and to be let off the hook.

If he was not a newbie, he would have known that postage cost from USA will most likely negate any advantage of lower price.  It is also possible he bid on both thinking he will be lucky to get one.

I did that when I first joined eBay and desperately needed a dog crate, and was getting outbid the whole week.  Finally, there were 2 finishing only seconds apart,  so no time to bid on the second if I lost the first.  And none in the right size listed for days, so I bid on both, and won both, and paid for both.  Fortunately, a friend wanted one as well, so I was able to sell it to her for what I paid for it. 🙂