Ask HN: Bitcoin – Possible 51% attack on 4/20?

https://blockchain.info/charts/n-orphaned-blocks I was browsing the Blockchain yesterday when I noticed a massive spike in "orphaned blocks" that had occurred over the past two days. Previously, the number of orphaned blocks had been a constant 0. Starting around a month ago, the number of orphaned blocks began to increase. On average, 2-3 orphaned blocks were generated daily. On 4/20 the number of orphaned Blocks spiked to 151. This is coupled with a suspicious DDoS attack on Monday (http://newsbtc.com/2014/04/21/blockchain-info-services-due-ddos-attacks/). Was this an attempted 51% attack? Did someone try to fork the chain for their own nefarious purposes? I would appreciate any insights on this anomaly.