“Really?” she’d said, a trace of sadness in her voice. “Really, truly?” Billy and Papa nodded at the same time.
“I’m Dad,” said Papa.
Mama put her bag of school things on the floor, sat on a kitchen chair, and pulled Billy to her. She hugged him, and in the most natural way, said, “I guess you’re growing up.”
“Yup,” he said, squirming away from the hug.
The above paragraph is from the The Year of Billy Miller What is the meaning of the bold sentence？Does it mean that Miller has grown up? Why does the writer use present continuous?