Patreon will give that information to the government, if the government subpoenas those records. If the company does not comply with the government's subpoena, then the government will not allow the company to operate within that government's jurisdiction. So pretty much all companies, including companies which care about customer privacy, will go along with a government subpoena. In this case, however, the concern is not Patreon, but Mega.
No, Mega did not report anything to Patreon. Mega sent PaleGrass' private information to the authorities. And they did it on their own initiative. The government did not go to Mega and demand PG's information. The government didn't even know that PG existed. Mega decided that they were going to take down PG's account, and then they decided to voluntarily send his information to the authorities.
Now, Mega is based in New Zealand, and when they say that they're going to send someone's information to the authorities, they mean that they're going to send the data to the New Zealand Police, which is their national police service. PG does not live in New Zealand. He lives in Ireland, which might mean Northern Ireland or the Republic of Ireland. However, the New Zealand Police do work internationally with other law enforcement agencies, so, if they believe that something is a crime in your home country, they will forward the data they have to the appropriate police agency. This is why PG is concerned.