A 5-blade diaphragm on an older lens is not unusual, and it does not necessarily indicate a flaw or a special “Zeiss look.” The main point from the community answer is that modern concern over especially smooth, rounded bokeh became much more prominent later. In earlier eras, lens makers and photographers were often less focused on perfectly circular aperture openings, and the geometric shape of out-of-focus highlights or flare could even be considered desirable.

So the likely explanation is simply design priorities of the time: optical performance, size, mechanical simplicity, and intended use mattered more than maximizing a rounded aperture shape. More blades can help make blur highlights rounder when stopped down, but blade count alone does not determine overall image quality or even all aspects of bokeh.

In short, your Distagon’s 5-blade diaphragm is most likely a normal product of its era rather than a technical limitation or a unique signature feature.