You're right, he wasn't trying to obtain information — which isn't required for a rhetorical question, as the excerpt you quoted says.
He was emphasizing his opinion by voicing it as a question. The text immediately after the excerpt you posted says this makes a valid rhetorical question:
> ... or as a means of displaying or emphasize the speaker's or author's opinion on a topic.
He was emphasizing his opinion by voicing it as a question. The text immediately after the excerpt you posted says this makes a valid rhetorical question:
> ... or as a means of displaying or emphasize the speaker's or author's opinion on a topic.