there is no direct way of knowing this, but you can infer it. The selectionChanged eventArgs include useful information to achieve this. Check out the documentation here, specifically the startRow, startColumn, rowCount, columnColumn, those properties are basically the coordinates of what's been selected in your table/range. Also probably you already know this, but the Matrix and Table bindings have a binding.columnCount property that you can use in conjunction the EventArgs described above and doing some simple math you can infer if only one row is selected and if all the columns in that row are selected.
Hope this is not too confusing and useful for your scenario.
thanks!