Perhaps we are speaking to different things but the "PNG Sequence" is intended for creating an animated pictorial sequence of the animation of your Project. If there is no Timeline animation, however, You won't get anything other than what is showing on the screen when the Timeline is at zero seconds.
The "Advanced Export" is where You want to go to extract the actual images used in your Project. Please see attached file: "AdvancedExportScreen.png" below.
I deselect all the checkboxes under the "Scenes" panel (e.g. "Create enclosing folder", "Also save .html file") as shown. You could also elect to go into the "Include" + "Resource Name" + "Size" panel and uncheck all non-image files. But I think it is faster if You have a large number of files (which are alphabetized in this panel) to export them all and then in the Mac's Finder use "List View" and "Sort by Kind" to segregate the image files. Another advantage to using the Finder is the "PNG" files & the "JPEGs" are discretely separated.