Under Linux, the icon of imported models are built from the screenshot of the 3D preview shown in Furniture import wizard.
Therefore, you must be sure that the 3D preview of wizard’s last step (or the preview shown in the Furniture Library Editor) must be at screen and not hidden by other windows to get a correct icon.
Was it the case?

Note that double clicking on the bicycle you imported in the catalog will show again the wizard to let you update it if needed, its icon included.