Help! Horse kicking in horse lorry

So recently I took my pony out of our yard to go to a charity hack which was about 20 mins or so away. This was my first time actually taking him myself out of our current yard (I’ve only had him a short while) and my friend was driving me and him in her horse lorry along with her own horse. When I say lorry I don’t mean a big one, it can only take 2 horses and is rather dainty.

The journey there was fine and both horses were very well behaved. When we got there everything went as planned and the hack was perfect! My pony was moving faster than some of the sport horses, he was so fresh and happy!
But the journey home was slightly different.

It was all going fine until the last 5 minutes or so. The whole journey my pony had been eating hay from my friends horse’s net instead of his own and I think it got to a point where he couldn’t reach it anymore and he stopped eating. Then he started to get really agitated with my friend’s horse and put his ears flat back and started kicking the partition between them and actually kicked it out of its hinges. Luckily it wasn’t broken and none of them were hurt, since we were quite close to home again too.

But i’m not too sure what really triggered this behaviour or what I should do next time her travels?
My pony is a gelding who is quite old (22+ not entirely sure) and this behaviour isn’t exactly rare with him as he usually does the same this in his stable too and acts this way with almost every horse. But in the trailer its different as we are driving and my friend isn’t overly confident with driving with kicking horses in the back and the next outing is a competition and I wouldn’t want I’m getting himself hurt /:

We are definitely giving him a bigger net in the trailer next time as he didn’t touch his small travel net (My friends horse had a normal sized hay net) we were thinking that might have been the problem…
Is there anything else I can or should try?

Ship him alone. Not all horses appreciate being in close quarters with other horses in an enclosed space.

Agree with the above advice, but if it is not possible,

blocking your pony’s sight of the other horse, I have used blinkers with one full cup to good effect in a similar situation.

distracting the pony with his own hay,

using the same hay in both bags, may help.

It sounds like they were scuffling over the one bag of hay, that hay being the most palatable?