I guess we can safely agree that we’ve seen better images here, but sometimes you have and sometimes you don’t. If it’s for nothing else, it at least shows what the bokeh of the Sigma 70/2.8 Macro looks like at f4.
This lens has a nine-bladed diaphragm, but as you see, the blades are not curved and what we get for spotlights are regular nine-sided polygons (What’s that in English? My dictionary stops at “octagon”), not circles. This is much better than many other lenses and in general the bokeh is pleasing, but it is a thing that one needs to know. Fetishists may dislike it.
As you already have seen here, wide open at f2.8 it is of course circular, but that’s true for many lenses. Wide open their diaphragm is completely retracted and the bokeh is only determined by the barrel.