I think the distinction is that if those two pieces of code had a different idea of what a word is then that would constitute a bug, then you definitely need to

I think the distinction is that if those two pieces of code had a different idea of what a word is then that would constitute a bug, then you definitely need to replicate the 'how to find words' logic. But if it doesn't really matter if two different pieces of code are using the same exact way to do something, then that's likely 'coincidental' replication. If you need to do word splitting, and someone else has written a word splitter, by all means copy paste their code to get you started, but definitely don't assume the best plan is to pull their code in as a dependency.