I'll be more inclined to believe this specific claim (tiny circuit boards, 100,000 of them) once we start seeing pictures of them, teardowns, analysis, etc. 100,000 is a lot of units to keep completely secret and one assumes that the people who've been hacked don't all have an incentive to not say anything.
Yes, I'm inclined to take this news with a grain of salt (a very tiny one, mind, given the incredibleness of this entire situation) until we see some examples. As you say, you can't keep 100k devices secret.
(Although the truly paranoid might doubt the veracity of a claimed "tear down". It has become incredibly easy to accuse the NSA of doing anything, and at least be partly believed. Which, ironically, is actually a pretty good cloak of secrecy in itself!)
