River Fans are found off the mouths of rivers that have changed position in recorded history. We know it didn't involve floods in any of those cases, so there is no rerason to speculate that a flood was required in any case.
So9
The article didn't bring this out well, and I haven't read the book in quesion. But I think the problem with river cones is that none of them are as big as they should be if the earth is millions of years old.
It does raise some interesting questions. Why did the Colorado carve such a huge canyon, but the Amazon and the Nile haven't?