Those natives were shooting at them! And it didn't look like blanks. Any one of those shots could have potentially killed Picard.
Exactly. Which is why it looks like a setup. Because if it weren't, Picard would
It's the clumsiest "ambush" in the history of ambushes since Shurgor the Sneezer tried to hide in the poison ivy with his brave naked men (including the military band with all the cymbals and jingles) during the mosquito season. The natives had no need to fire from the move when first taking aim at Picard, nor a need to leave an escape route open for his buggy. And nobody went inside the shuttle with its open cargo door?
If Shinzon had access to an actual Soong android, and he was now the new Praetor, why didn't he just contact the Federation, tell them what he had, and specifically ask for the Enterprise to come to Romulus to get it? That way he'd have Picard and a way to get B4 onto the Enterprise, without resorting to wasting time on Kolarus.
The way the events transpired (regardless of whether it was Shinzon's doing), Picard was not invited to Romulus
. Rather, Starfleet sent a "random" ship with a "random" skipper. Which might be important for Shinzon, whose explicit and sole goal was to invite Jean-Luc Picard, the man on whom his own life depended.
On second thought, why even bother with B4? If Shinzon needed Picard's blood to survive, why didn't he just contact Picard and tell him this?
Shinzon was the product of a Romulan plot to duplicate Starfleet personnel. The Romulans no doubt also wanted a Soongian android of their own, either as part of this program or then in an unrelated effort. They would have tried to acquire one, or build one; and while B-4 was a failure in that regard, he would naturally have come to Shinzon's attention through the duplication program.
Why not use B-4? As said, Shinzon wouldn't have wanted anybody to know about his need for Picard specifically (you don't reveal your one fatal weakness early on if you are an Evil Overlord, and the fairy godmother wasn't around to reveal it, either), so asking was out of the question. But with B-4, he could kill half a dozen birds with one stone. Or hammer, as it's probably also a case of "everything looks like a nail": Shinzon, a tool in an agent insertion program, would now complete the project to insert a Soongian agent aboard a Starfleet ship! He gets Picard, he gets access to Starfleet data, and in the best-case scenario, he even becomes
Picard and might be able to take over the E-E - either as a further tool for his nefarious purposes, or then as a Plan A that secures his retirement (with the wrecking of everything in vengeful anger, starting with Earth, being but a Plan B).