When you create a SOLIDWORKS Indented BOM from an assembly that contains sheet metal or weldment parts it will add further indented rows with the cutlist information. You have the option to show the ‘Detailed cut list’ in the Indented BOM. For weldment files, deselecting the ‘Detailed cut list’ option will show the total length of each structural member size. When you enable ‘Detailed Cutlist’, it will break it down into each cut list item with the quantity.
If you also have a Sheet Metal part in the assembly it may only contain one body. The extra row will be included as a Sheet Metal part can have multiple bodies and separate cut list items. The Description in this row will pick up from the Cut List Properties in the Sheet Metal Part.
NOTE: The overall part files in the images below have no Description custom property applied which is why they have blank cells. Only the Cut List Items have a Description property added for clarity.
If you need to use an Indented BOM from the assembly level but only want to show a single line for the Sheet Metal part, you can expand the BOM panel on the left and collapse the Sheet Metal item.