I think what might not be clear in those guides is that the columns have to be structured with sequential numbering in a Google Sheet. It’s a very specific method.
There is a reason that you can’t assign row owners to a column the way you are trying to do it. In glide, any computed column is actually computed on the end user’s device. What that means in respect to row owners is that your row owners would not be able to be verified until AFTER all data is sent to the user’s device, where the array is then computed, and then row owners can be checked. Obviously, if you have already sent all data to the device, then row owner security is not really applicable since it’s too late and security has been compromised.
The only type of array that can have row owners applied is one that is build using the sequential numbering method. This is a bit of a hack method, and the array is actually computed server side instead of client side. For that reason, you can apply row owners to that type of array.
I think a better way in your case would be to just apply row owners to two separate single value columns. Then you don’t have to mess with making an array, and it will work as expected.