I don't know where you got the idea from that it would work like this.
A find_by() always does a value lookup, you can not use any other operator. If you want that, code a normal find() with a where clause. And what are the 5 and 10 arguments? Not sure what you intend to do there.
If you pass a third argument, it has to be the options array, like you pass as the second argument on a normal find.
I think you are mixing \Model\Crud and \Orm\Model which have different implementations of find_by(). The OP seems to be using a class deriving from \Orm\Model, however, the doc you linked mentions \Model\Crud which obviously are different classes.
So check the implementation of the model in question and see what it ultimately extends - \Model\Crud or \Orm\Model - then you know what to look inside the docs for.