DDOS still has to go through hops. It doesn't just magically show up at the server... Since it seems the servers are near level 3 hops, it would make sense that a DDOS would end up both affecting the server AND level 3 traffic. Level 3 having issues is an indicator of either bad switches, or an overload. A DDOS powerful enough could cause the 2nd so if anything the level 3 issues were an indicator of a possible DDOS that was packeting through their hops.

Which in the end - still not SE's fault