Almost every summer he thinks: This is the best summer. But this summer, he knows, really is the best. And not just the summer: the spring, the winter, the fall. As he gets older, he is given, increasingly, to thinking of his life as a series of retrospectives, assessing each season as it passes as if it’s a vintage of wine, dividing years he’s just lived into historical eras: The Ambitious Years. The Insecure Years. The Glory Years. The Delusional Years. The Hopeful Years.
— Hanya Yanagihara, A Little Life
I’ve read that you don’t have to, grammatically, write a complete sentence, and then write a colon.
In And not just the summer: the spring, the winter, the fall., I don’t see a complete sentence, then a colon, and I don’t see a complete sentence used after the colon. There may not seem any utterances, which I think I’ve read may get used.
What may you call this, in grammar?