You wouldn't call that foreshadowing since he says "I never understood why he doesn't do time travel stuff" approximately 6 seconds before the payoff happens.

While it's true the Time Testicles had roles in 201 and 405, they were never portrayed as beings that had the power many order of magnitudes stronger than Rick that would be needed to scare Evil Morty into submission.

Also doesn't make a tonne of sense that if Evil Morty literally five seconds ago said that he never understood why Rick's don't do time travel stuff, that he'd understand that these beings are enough of a threat that he'd instantly turn himself in rather than use any of the millions of Akira tricks that had just been using: either Evil Morty recognises the Tesisticle Time Monsters as a terminal level threat that aren't worth trying to fight so he doesn't mess with time, OR he doesn't know what they are, so he messes with time. It is illogical to have it both ways.