I strongly doubt that those Bitcoins come from a hack or any other illicit activity. Market sell, or OTC, Galaxy must do a thorough KYC on the party they need the sales for.
If the funds were tagged as a result of a scam, it would be impossible for Galaxy to trade with them.
That is most probable, but what if verification is not possible? I doubt they would not finance such a big sell, but my thought of Wall Street is that they look the other way if necessary.