Nuance of "announce" not say/tell ; could be bothersome

Hi,

Would you describe the difference between announce and say/tell? When I looked it up, all the dictionaries basically say:

You tell something "publicly or officially"



But in the book I'm reading, there're announces that seem not agreeing with the definition. And the below is one of those.




I was a few minutes early one week and entered the office to find Agent Samson doing her job on Garth Barclay, a slight, kittenish boy I'd met back in the fourth grade. "You may wait outside in the hallway until it is your turn," she told me. A week or two later my session was interrupted by mincing Steve Bixler, who popped his head in the door and announced that his parents were taking him out of town for a long weekend.



To my ears, said (not told) is proper enough. What is the difference? Why is the author using "announce" instead?



Thank you,

M