Yes, I am not saying it doesn't happen, only that it should not be allowed to happen. One nation willingly subjecting itself to the jurisdiction of another nation in the realm of civil justice is ludicrous and overreaching. The United States should not honor verdicts in EU civil lawsuits, nor should the EU honor civil suits adjudicated in the United States. Doing so is a bastardization of sovereignty. I would make an exception for products, goods and services a US company sells on foreign soil, because once that company has a presence there they willingly subject themselves to the rule of law in that nation. If they don't have a presence there and the products, goods or services are not offered locally, there should be no jurisdiction.
I despise Facebook, Twitter and Google and would love to see them go out of business, but they should not be subject to any regulations that apply in another nation when a foreigner chooses to register an account on the internet where the site owner and domain is US-based. If this becomes a serious problem and the national leaders remain feckless in blocking it, then those companies would be wise to take appropriate measures to block registration and memberships from outsiders.
Even criminal prosecution should only be honored if and when it violates United States criminal code, and it should be tried on American soil with the same due process it would have received if the crime were committed in the United States. The EU conviction should not be ignored, but it should be sustained only to the extent it violates US code and goes through the same trial process and is decided by a jury. That is usually not an issue because the really serious violent crimes are illegal in all civilized nations. The exception would be if the crime is committed in the EU and the suspect is apprehended while in the EU or extradited for prosecution in the EU (where such an agreement for reciprocity exists). One example of this would be a violation of Sharia Law when the act is not illegal in a nation that does not observe Sharia Law.
If I had to guess (and we have no information, so all we can do is speculate,) that would be my best wild guess. You probably nailed it with that one, but we may never know the real story.