I spoke with Tecfan and they don't remember what exactly happend two years ago. They were assuming what might have happend, based on the way the dispute was created,assuming they might have lost a game but not being sure of that.
From my conversation with Higgy Baby they told me that as far as they remembered they went first with their key but it turned out to be not working, so they didn't use Tecfan's game.
Higgy Baby also provided screenshots of their ''license and product key activations'' from activation of Why So Evil 2. It shows that that game was added to Higgy Baby's library 3 times on two different dates. It also shows that all those three times Why So Evil 2 was added as part of bundle with two other games ( Brilliant Bob and Why So Evil ) and none of those tree times Why So Evil 2 was activated as individual game.
The first date Why so Evil 2 was added to Higgy Baby's account was 2015/06/14 (37 days before this offer was created).
The second date Why So Evil 2 was added to Higgy Baby's account shows to be 2015/07/28 - 6 days after Tecfan had failed the offer with Higgy Baby
I asked Higgy Baby why the game was added three times to their account and they forwarded me to this thread - http://steamcommunity.com/app/354850/discussions/0/142261352649771017/
It shows that the developer has been adding Why So Evil to the libraries of Why So Evil 2 owners and vice versa. That explains why the game was added twice in Higgy Baby's account on 2015/07/28.
In any ways the first day shows that Higgy Baby already had Why So Evil 2 in their library before initiating any offer with Tecfan.