According to Bloomberg's report, these coins were seized by the US government and it is confirmed that the coins were not hacked.
What remains the real question is why right now this hacker has decided, as they say, to hand over what he has kept for years? Obviously there was that
“money or life” thing, but again the question remains why the hacker didn’t try to disguise the trail and save the BTC for himself, because he had years to figure out how to do it. He could be a hero, a digital Robin Hood who could anonymously make tens of thousands of people happy and share everything with them, which would certainly be nobler than rubbing the neck of a fat goose. At least we see that the US is in step with the technology, they use a native-segwit address
It seems that the US isn't just in step with technology but with enough of a trail, they were able to gain access to the so-called "Individual X" and somehow had enough leverage on him to pry those bitcoin out of him. That is pretty scary. It also doesn't feel like that "Individual X" was much of a hacker. If he had been, this condition would not have arrived that the authorities traced the wallet's owner and then forced the keys out of him. He was probably someone who just happened to be in possession of the wallet but found himself in the clutches of authorities, either recently, or maybe from the beginning.
With the ~144,000 BTC initially siezed from Ross/ Silk route, the total stands at over 210,000 BTC that the US authorities had access to due to the Silk Route investigation. The mystery now is the capitulation and fate of "Individual X".