A tube may not be sheet metal, but this is a moderately clever abuse.
Since the target use for the information is a laser tube cutter and a laser can't make decent tapered cuts in what is essentially rolled metal sheet tubes, the sheet metal module is a decent tool for this application.
That said, it is pretty far from what usually counts as sheet metal fabrication, so the lack of ability to deal with things besides simple cuts and extrusions is not a total surprise.
I'm curious as to the difference it makes. When it is time to program the cuts can't the software be told which edge to follow? Right now it looks like the primary surface is the OD of the tube. If the curve on outside is followed, the tubes can't butt together without grinding, which will leave a knife-edge. Following the ID curve will allow them to fit and provide a decent edge to weld to.