Yeah usually such outages are a result of a IT nerd somewhere pushing a few wrong buttons.
For example there is a story where Iran tried to block you tube by redirecting its IP to nowhere. So in order to do this there ISPs added an extra entry into there routing tables of there internet routers, so this was a high priority route that says "Youtubes IP is this way". And it worked, youtube was now inaccessible since all traffic to that IP was now routed into the abyss. However they made a slight configuration mistake that made the router start advertising this new route to other routers and since it was high priority it yelled out "Hey everyone, i got a nice short route to youtube on my network" so other internet nodes wrote down this entry. As a result internet nodes in countries near Iran found this fake route to actually be shorter than the route to actual youtube servers, so they started sending there traffic to there as well, bringing youtube offline in those countries as well. A few hours later they realized how big of a mistake they made and quickly removed that routing table entry.
On a small scale i made a similar mistake. I was hosting something, so i was forwarding ports on my more enterprize-ish router. However on the large page of like 50 settings for the routing entry i got one of them wrong. It all worked fine, i could access it, everyone outside could access it, great, job well done. However later on i found out that i could not connect to other servers... odd... they don't seam to be down or anything so it should work. Then i figured out that not only have i port forwarded the internet traffic on that port, but i also mistakenly port forwarded all internal LAN traffic on that port as well. DOH!!!
All it taken was one wrong configuration setting.
EDIT: By the way. The reason most home networks don't have issues like this is that most home routers only give you the basic settings, you give it the port to forward and the IP and that's it. But more professional networking gear can have massive walls of settings for seemingly simple features. This makes it flexible to do nearly anything you want. But at the same time it makes it easy to make it do something really stupid if you punch in the wrong stuff, the router will simply follow your stupid orders.