No, it isn't clear and often people state something off the cuff which isn't true at all, especially in texts and facebook postings.
I just think the gun aspect is interesting, not for TY - she could be "annie get your gun" for all I'd care, it is more to do with David owning guns.
David and Tiffany were not unaware how dangerous Mexico could be, they lived there for a few years, they were aware of how dangerous the lake could be. David and Tiffany both talked about a plan should they be confronted by pirates, alleged by Tiffany anyway.
I'm just wondering if he took a gun with him when they went to the lake and if he did so did he use it and cause the pirates to fire on them in return.
What about this scenario - The pirates come towards David and Tiffany, they both get scared and drawn a gun, maybe fire a warning shot towards the pirates and then all hell breaks loose. Maybe the gun wasn't registered, maybe Tiffany could be concerned of getting into trouble if they fired first.
I don't believe Tiffany set this up to murder her husband, maybe she could have done it accidentally by firing back at the pirates. This makes sense to me more so than anything I have heard so far.