I don't think recruitment spam really counts as "in confidence." Certainly he's under no NDA. I guess some might consider it rude, but I wouldn't.

He said it was the recruiter's initial e-mail. If someone e-mails you out of the blue with details like that I think you're more than allowed to tell others about it.

I don't think email is considered confidential by default. Had this recruiter made any confidentiality request, I would have tried my best to honor it. Instead, he seemed more interested in spreading the word that they were entering the search game. Also, Apple has not been exactly hiding their growing interest in search. They rarely let their engineers speak in public, but they were on stage this year at Lucene Revolution giving a number of details about how they are using Solr.