Yeah, I looked again and it looks like they're actually only pulling those packages in when they need to build node for the current ARCH. (that's what I get for just scanning to the first call to apk add)
They also appear to be cleaning them up, so I'm not actually sure where all that extra weight is coming from.
Node itself is fairly trimmed down in the packages for alpine (40MB installed), but they're not using that package, they're pulling in their own version from their download sources - so it's possible they're including a lot of extra junk there. They also add yarn which is another 10mb.
But in general - I agree, there's about 100mb of weight I can't actually explain in that image from a very quick look.
