What? I can see how google would know that you own all the blogs (because your adsense code is on all of them) but it doesn't link them together. Is that what you mean?
He's referring to the fact that Google will know they are all linked to you. So if you break the Adsense TOS on one of them by, for example, letting some inappropriate content slip through and google punishes that blog. They will punish all your blogs, by either de-indexing them, or banning you entirely from adsense.
In other words, if you didn't have adsense on the blogs, and google decided to de-index one of them for any reason, possibly spam, then it wouldn't affect your other blogs.
Something to think about...
BTW, some people may be getting confused with autoblogs and cycle sites. Cycle sites are sites where you spam the fucking shit out of them by putting up ridiculous amounts of content in a short period of time (ie. 500 posts/videos per day). The reason they are called cycle sites is because they last only a short cycle and their done. You definitely don't put adsense on this type of site, instead some other cpa or contextual advertising, but the main point of it would be link building. A typical site of this sort would last approx. 3 weeks before you should take it down (don't get greedy) and stop posting. But in those 3 weeks you would build an insane amount of links and probably a very nice chunk of change

. now create large batches of these cycle sites, as they are very quick to make using simple rss feeds, and cycle them out every few weeks. Essentially you will be creating thousands of niche specific links you can later use to power your white hat/straight affiliate sites and start stacking some real chips

Maybe you guys have seen this topic covered on Eli's Bluehatseo Blog, which is where i learned about it from. If not heres the link (amazing blog, if you haven't read it yet, GO NOW!):
Read this fucking article and say thanks (cycle sites are covered in it):
PHP:
http://www.bluehatseo.com/seo-empire-part-1/
Autoblogs on the other hand, should have quite a bit less posts are has been mentioned in this thread, however, I would still be wary of putting adsense on them. Maybe someone with more experience can touch on the topic of adsense + autoblogs a little more in depth.