I have found that there is a bug when working with tables in the editor in inline editing mode in Safari on Mac - https://demos.telerik.com/aspnet-ajax/editor/examples/inline-editing/defaultcs.aspx
In the normal editing mode, you can edit the table properties by right clicking inside the table to get the context menu, then choose table properties, add row etc.
In Inline editing mode, it shows the context menu but when you click on any item it says to select the table. None of the other context menu commands like inserting rows etc work.
I have tested on your demo site and you should be able to simulate it there.