https://www.irs.gov/pub/irs-drop/rr-19-24.pdf

The IRS considers a hard fork the creation of a new asset class. One cannot steal an airdrop since the property is newly created and has never been in the possession of the legacy wallet.

Justin's claim that anything was stolen is ridiculous. If he is referring to the Steemit Ninjamine stake, I'm fairly certain, that was just temporary frozen, and recovered in its entirety over 3 months ago.

As for assets being frozen. Cryptocurrency Exchanges and blockchains do this all the time, intentionally or not.

However, as for assets being seized, something hardfork 23 on Steem intends to do, this is entire without precedence and most certainly theft.
I feel sorry for the people affected. Please resort to legal recourse first.