I guess it depends upon the use case. If each item is a cell, with everything it needs in one atomic unit, then probably top to bottom is best. However, if, as your example suggests, the cells relate to each other in some "flow" order, then, as long as the intended audience is used to a Roman/Cyrillic script system, left to right is better from a user point of view.
I have a feeling that it is being objected to on the basis of technical implementation. I had a massive epiphany a few years ago, when I switched from an "engineering-centric" model to a "user-centric" model, which can be more difficult to implement.
As NNG is constantly saying, a user study is the only way to really answer your question. However, if the client that is paying the duckets wants it one way, then they make the rules...
Post your resolution here. This is an interesting conversation.