I don't know what it is, but betta's have never really appealed to me. I think its several years worth of anoyance over the volume of posts in the TFF betta forum "spamming" the recent posts list that's put me off
I used to have a Betta identical to yours in my tank.
I used to get tired of people going about Bettas being non community etc so I stopped visiting the betta section of TFF. Too many 1G merchants in there with teir 'barrack' setups.
Mine used to love running around a nice large tank and was very fond of a female black molly. lol.
I should think in a large tank they would be much the same as any other territorial fish in that as long as there are plenty of plants/hardscape to break the line of vision that they can settle on sharing the tank. Betta owners would probably say that your tank was too large though lol
I had a fighter that I bought as female to breed with my male. Turned out to be another male and very nearly killed the other one. Added it to my community tank where it attacked a male ruby barb taking out one of its eyes I took it back to the shop after that!
I've had others which have been quite peaceful. I'm guessing it was more of a throwback to the short finned wild type which are more aggresive.