It's a small group of people, there's a combination of different protests going on. A lot are protesting actions by the government (namely allocation of resources to tourism instead of healthcare, but that's a complex situation with tourism being the only way they can afford to import healthcare products).

The reactionaries saw this "discontent" and decided to jump on it thinking it was anti-communist when it was actually just people practicing direct democracy as is allowed in the Cuban constitution. The reactionary agitators started fights and hurt people, it now seems to be mostly under control and there's local discussion about the actual concerns that started the protests (resource allocation).

The gusanos in Miami are perpetually waiting for a chance to do Bay of Pigs 2 because they want Cuba to be a semi-feudal mafia state again. Ever since Kennedy told them to chill and they killed him this is all they've ever wanted.

Also, the new season of Blowback basically pre-emptively debunked this whole thing lol.

Another point is that the people in Cuba aren't idiots. They know that leveraging their government is a good way to change policy they feel is poor or wrong, but they also know that the ultimate cause of all their economic issues is US embargo. No one thinks letting the US in would improve things. Mainly because there are still people alive who lived through the last time the US was in control and had the fascist Batista running things.