That analysis showed that supernovae are almost certainly not the source of the actinides.
This conclusion is based on a reasonably long chain of logic.
These rocks have floated around the Solar System doing basically nothing, at least until some of them had the luck to land on Earth.
Over that time, the radioactive elements will decay, leaving behind stable isotopes of different elements.
But the numbers simply don’t work out: if actinides were produced by supernovae, it would lead to a higher abundance of these elements than we actually observe.
On the other hand, the researchers are also able to estimate the number of neutron star mergers that could contribute material to the formation of the Solar System.
We've only observed one neutron star merger at this point, though, which leaves things a bit uncertain.
You might think that since most stars are pretty much the same, all star-dust is equal.
But we have evidence that some star-dust is more equal than others.
Neutron stars are (from a computational point of view) nearly ideal stars, so we can model their behavior pretty well.
Combine those models with our observations of a single neutron star merger, and researchers have a pretty good idea of actinide production.