I mean naturally yes it is but it takes a good league player as a whole not just being a jungler to be a good shot-caller. For example, i wouldn't want a jungler who only play's jungle to shot-call, if they haven't played the other roles then they don't understand what the other roles are going through and can't help them towards obtaining victory.
To be a good shot-caller you need to have a grasp of everything in the game, your micro and macro play needs to be on top of everyone elses, you need to know where everyone is going to be at crucial times and where your team needs to be at crucial times. Faker and Bjergsen aren't just good shot-caller's in LCS but also in solo Q, Bjergsen is arguably better at it than faker as well considering how often Faker dies to ganks that he didn't see coming. Bjergsen knows exactly what to do and where to be, how to play his lane and what his allies are going through, so "naturally" he's the best choice to be a shot-caller.
For anyone to be a shot-caller you need to have all those things, it takes much more than being a jungler to be a shot-caller. Just because a jungler is responsible for map pressure(mainly) doesn't mean they're responsible for shot-calling because it takes more than just map pressure and awareness to shot-call.