I see what you mean, and this is true in most cases with bipinnate leaf structures, like Kentucky Coffee trees, for instance. But Actaea is far more confusing....
Any "normal" person would say this plant is opposite leafed from this pic below, but look again....
See where the peduncle (floral stem) junctures? A real stem has to extend at least to there. So this "single" stem could actually be a multi-stem structure. Not sure, though. It could just be one stem - the central portion (that everyone would call the stem) that terminates where the peduncle originates.
Likewise, the floral stem does not arise from the "central stem" in your copied pic above either, but originates in a similar manner.
It's pretty clear that Mother nature doesn't follow man-made rules!
