So it seems that selfish agents only engage in causal trade but that altruists might also engage in acausal trade.

We can't quite say that. It is certainly much simpler to imagine scenarios where acausal trade between physically distant agents occurs if those agents happen to care about things aside from their own immediate physical form. But off the top of my head "acausal teleportation" springs to mind as something that would result in potential acausal trading opportunities. Then there are things like "acausal life insurance and risk mitigation" which also give selfish agents potential benefits through trade.