What Determines Who You Can Trade With In Champ Selection

Are your trade options completely random or is there a set order?

I was just in a champ select where i was going top and i was 4th pick. I was going to use Volibear and had him shown as who i was going to use.

When it came time for 3rd pick to pick he picked Volibear without even saying anything to me 1st. And then asked me if I had Sona.

The only reason I can think of for him doing that was maybe he wanted to see who the other team was going to pick as their support.

So I picked Sona....but after all champs were locked in, neither of us got the trade option to initiate a trade with each other. usually I get 2 or 3 options but this time I only had the option to initiate a trade with our 5th pick.

I would of been fine just playing support but he ended up dodging.