If they really believed that their process eliminated any licensing conditions, why would they limit themselves to open source projects?

High quality decompilers have existed for a long time, and there's a lot more value in making a cleanroom implementation of Photoshop or Office than of Redis or Linux. Why go after such a small market?

I suspect the answer us that they don't believe it's legal, they just think that they can get away with it because they're less likely to get sued.

(I really suspect that they don't believe that at all, and it's all just a really good satire - after all, they blatantly called the company "EvilCorp" in Latin.)