It is not surprising. These price changes work both ways. Products have an overall level of demand, and they can behave flatly or wildly depending on price fluctuations. The more X1 is able to sell on holidays, the less it's going to sell outside of them. Because if in one year there are (examples) potential 6M US X1 customers in the US vs 8M potential PS4 customers, the X1 can win some NPDs but will lose the rest and the overall battle. The brunt of the sales are allocated to a specific period. That's why if you want to have a truly objective view of things, the gap never became truly higher than 1M nor was it ever cut down by the X1. It was small at the end of 2013, and it grew to over 0.5M at the end of 2014. Now it remains to be seen what its progress will be at the end of 2015. I have no doubt it'll grow until the holidays, but we'll see how much demand will remain for the X1 in that holiday season, same for the PS4 in case there is a price change.
But X1 fans are still welcome here, after all it seems to be doing better than before when the price was back to 400. That should count for something. Sales should be enough to keep major american publishers more satisfied than they were last year. Plus, if thanks to this some of the monthly gaps are smaller, X1 has a chance at one or another NPD. For example, August. Last year the gap was only 30k thanks to Madden bundle. Until Dawn might not be enough to fight a 350 dollar Madden bundle, giving X1 a win. Though, of course, a summer price drop from Sony could turn that around.