We only know four things for sure:
a) 450,000 Dash were stolen from Cryptsy
b) All those 450,000 Dash were sold over the last year
c) All those Dash are now gone; the dumper has exhausted his coins
d) 450,000 coins dumped on the market over the course of a year would have a significant impact on the price
Beyond that, who knows what market manipulation may exist behind the scenes. Still, there are now tens of thousands fewer coins per month being dumped on the market. That is going to have some effect. Maybe not $2.25 (November 2015) to $4.20 (January 27, 2016), but definitely *some* effect.
Regarding (a), from what I've read, Cryptsy hasn't said that their DASH were stolen. So there is high probability that Cryptsy itself sold the DASH to pay out BTC and LTC withdrawals, creating an "oversold" market situation.
IIRC the Bitcoins and Litecoins that were supposedly stolen, didn't move after the "theft" or theft. They were just directed in some addresses and they were stationary there for all this time. So if DASH was stolen and sold, then it would break the pattern of the thief. If he wanted BTC, he already had them, so... no need to sell DASH to get BTC. Therefore, if we accept the theft story etc etc, it makes more sense for cryptsy to have sold the coins and this is consistent with 1) what cryptsy said 2) the state of BTC/LTC funds that were supposedly "static" after the theft versus DASH which was gradually dumped.