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In general transforms don't have direction so representing them with arrows is not standardized. The particular level of ambiguity is that the transform for coordinate frame A -> coordinate frame B is the inverse of what it would take to transform a point in A to be a point in B. This is why the API all use source and target frames to specify that the API is referring to changing a reference frame.

When computing the transforms to publish it's more common to think about the transforms between the coordinate frames themselves and thus think about the inverse of what a lookup call will return.

So long story short it would make sense to turn the arrows around on the amcl page to be consistent with most representations. But you should understand that the only important thing when you draw the graph is that it's a tree with the arrows in a consistent direction. It's a bit of a users preference which way to draw the arrows. Since most other usages are drawing them this way consistency is the main reason to pick a direction.