DSS is EU-owned library I believe. I used it instead reimplementing digital signature verification for XMLs, PDFs, hadling certificate revocation, etc. Makes sense that they want to secure own library that secures many other applications.
WSO2 is Enterprise Service Bus that I used at another company (owned by government BTW) instead of one from whoever-makes-commercial-ESBs.
WSO2 is more than just Enterprise Service Bus. There are a bunch of products and solutions belongs to WSO2[1]. Enterprise Service Bus, API Gateway, Identity and Acess Manager, Analytics and Stream Processing Server are the core products.
As others have said, they are most likely being used by the EU in some parts of their infrastructure. Then the question becomes "Why were they using these software in their infrastructure?" The answer to that is probably along the lines of "a guy that was assigned to project used it because it came up in google," if I were to hazard a guess.
WSO2 is Enterprise Service Bus that I used at another company (owned by government BTW) instead of one from whoever-makes-commercial-ESBs.