Yeah, I'm not sure how Toshi would have accidentially run into the bodies, they're not on the route from the room he's in to the fight. So, yeah, I think he does need to explain why he headed in that direction or else edit it.
As for you being first, though, whilst you're right that Lantz has posted twice with Toshi since you last posted with Mille and Lancer, Toshi hasn't been interacting with them (indeed, you posted twice with them between Lantz's previous two posts), and Magos posted about five times with Jack in between Lantz's posts, resulting in him doing something that Lantz specifically didn't want to happen, so I don't think you can really complain on that front. There was no indication that Mille and Lancer had any intention to go towards their bodies and no real reason why Lantz should be expected to wait for your post.
Also, I don't think it is "metagaming", Magos has shown no indication that he intends to drink their blood, and Toshi does seem to value respecting the dead rather highly (plus, attempting to heal them makes perfect sense), although I guess he probably should explain why exactly Toshi felt the need to put that barrier up without reference to OOC knowledge. But, if he can do that, the only issue I see is that there is no reason why Toshi would even find the bodies if he's heading for the main battle (and, if he's not, then his challenge seems rather weird). The "disturbing the crime scene" argument is not valid, either. Attempting to save a life is way more important than that, and the barrier if anything helps preserve the crime scene.