Column text is a type of multi-line text that adjusts pieces of child text as columns within one multi-line text body. When you open a DWG file column text becomes a normal cell named "ColumnText", which contains pieces of child text located at their adjusted positions. To edit any piece of column text, you must use the Drop Element tool to drop the cell. When you save the change back to DWG, the dropped text remains dropped and is no longer a type of column text.
In AutoCAD, column text is a type of mtext. If you want to check whether the mtext is a column text in AutoCAD, open the mtext in an mtext editor and check the first icon on the mtext window; if it is not a column text, it has the selection of "No Columns", otherwise it is a column text.