I don't think Gale killed the goblins. There's zero reason to think he did. He was, as he says, swept from one rune to the next. I don't think he was even at that rune when the goblins were killed. He just appeared, after all.
He was probably at the rune that leads to the camp area. That's my guess.
The goblins are there to showcase that goblins are in the area. They probably saw the ship crash and went to investigate. At which point, they more than likely died in the resulting chaos. The place is full of fire and debris and had intellect devourers running all over attacking everything they saw.
The fact that there aren't any intellect devourer bodies there just means they killed the three goblins without taking any casualties.
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So, yeah. Shadowheart talks about the intellect devourers. The dead bodies that talk mention the chaos and the "brains" everywhere, running around, chasing people. There was fire all around from a giant ship that just crashed.
And Gale mentions that he came from another rune.
I'd say things are reasonably explained.
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You can even make reasonable guesses about things like pods. Astarion is right beside a pod, probably the one he was in on the ship.
The pod that smells like sulfur is probably the one Mizora was in... especially considering Wyll's interest in the pod if he's with you when you come across it.
It's mentioned somewhere that Wyll got to the grove a little before the player character did.
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Now, if you happen to sleep for a week and then finally meet Gale and want to know what he's been up to for a week... that's asking a bit much.
What if you decided to long rest for a month? Would you then want a full story from Gale about what he'd been up to for a month?
The number of long rests you take are variable and not something the game's story can reasonably take into account. Gale can't change his story depending on how many long rests you took, so it makes much more sense to keep it somewhat vague, but easy to make assumptions about.
