Hive was a newly created asset. According to the IRS (US tax authority) All cryptocurrency forks are new assets and any airdrop is also considered a new asset. Therefore, not airdropping someone is not theft.
Although in theory it may have existed in your wallet before it was removed, you never control any Hive in your wallet.

This is not the case for Steem. What is happenening here is clear cit theft.