Well the causal relation there is speculation. The thing that seems odd to me is the shooter seemingly went to great lengths to avoid sending a message - hiding their identity, issuing no public statement, etc. If this was over a denied claim that they threatened over, why bother hiding their identity? It would be trivial to figure it out based on the claim.
Then you have the fact that the shooter apparently used a silencer too and cleared a jam quickly. Seems like rather than a disgruntled nobody sending a message, this seems more like someone trying to make him go away as efficiently and quietly as possible.
So alternate theory: The victim had a lawsuit filed against him by the DOJ related to an anti-trust investigation and insider trading. What if he decided to make a deal with the DOJ, and somebody else found out and didn't like it?