Rad hard parts are basically never sold through distributors. Strict lot traceability is a requirement on space programs (to avoid the issue discussed in the article). The quality departments at the manufacturer and buyer also need to communicate a whole bunch of stuff (requirements, test reports, etc) which defeats the purpose of the insulating layer of a distributor. Also, while these parts are expensive (my rule of thumb is to add 2-3 zeros to the cost of a commercial part to estimate the cost of a rad hard version), they are low volume, so there's not a whole lot in it for a distributor. The contractor working on the electronics almost certainly purchased these parts directly from Infineon, and Infineon would have had records of who purchased parts from which lot.
The fact that they found out about this accidentally at a conference is, all by itself, extremely strong evidence that Infineon didn't notify whoever they should have for the Europa Clipper mission, whether that was NASA itself, an in-house contractor or an external subcontractor.
