Ken - I saw this statement in the book, also, and don't know quite what to make of it.
Reaction wood is a descriptor for the larger spacing of growth rings on one side of the pith relative to the other on branches. There is a difference in how the wood reacts as it's drying, which explains the name.
I'll have to dig into the literature to see if there is a difference among plant families in how the branches put on secondary growth. If the above statement is anecdotal in nature, it may just be referring to differences among plants that typically occur in one hemisphere vs the other.
Andi