The tweet says it all, and I think we can probably concede that if Daddy Gronk says it's happening, it's happening.
After earning All-Big 12 accolades last season, Gronkowski was largely supplanted by Winston Dimel this year. We can argue about the reasons, but the effect is clear: Glenn sees no reason to stay in Manhattan another year now that he has his degree.
It was widely speculated that Gronkowski was leaving Manhattan, but most assumed it would be via transfer. That he's going to the NFL is a mild surprise, but not a huge shock.