Of course they didn't. Because they were never there. If they were, I'm sure he would've signed a NDA because Apple engineers driving around town and going to someone's house after the dude posts a blog is downright creepy.
I used to work for one of the largest server/PC manufacturers in the world and had the job to recreate customer issue in the lab for engineering to document and fix. While job was for large scale sever infrastructure; if I had to visit a customer site to figure it an issue we never had to sign an NDA because I kept my mouth shut. The only thing you sign an NDA for is a alpha release fix or you are getting a special or early release hardware. Troubleshooting is pretty universal and isn't secret.