While it might be ok to use colloquially the term, "Fenwick trees" since it became a common name, calling them "a Fenwick's work" and not mentioning Ryabko is a clear misattribution.
That said, as far as I remember, I did not know about Ryabko. So while it might have been a misatribution, it's far from a clear one.
Did he publish it btw.? If so, do you have a reference?