By Solomonoff induction, we should suspect we are in the matrix if we can find a mathematical description of a simpler universe that simulates ours even when taking into account the loss of simplicity that results from having to precisely identify our own universe simulation in that other universe (having to identify the simulation prevents all universes from being reduced to the simplest universe which simulates all possible universes).

Although, in the terms of Solomonoff induction it only even makes sense to ask the question if being in the simulation makes a testable difference (i.e. interference from outside entities or we are fated to break out).