This is Echo-san's domain. It's all but certain we are being watched at every moment. In that case, it's not so difficult to believe such a powerful entity might be able to revive a person from their instant of death.

[Though the implications are a bit alarming when he considers that Sam's corpse was supposedly literally eaten, which either means 1) Hannibal was lying 2) Echo has the power to recreate an identical copy of a dead body from scratch and replace a consciousness within it. Occam's razor would suggest the former explanation, but he'll reserve judgment for now. More important is the following:]

But it's considerably different if Echo is able to reverse death outside of those parameters, from various worlds with different metaphysics, which presumably aren't as readily monitored in real time.