It would make you to wonder why this Bybit hackers decided to send a few of their loot into centralized coins. It could be a test transaction as you said, a little something that they can sacrifice to forfeit.
Tether and Circle were low balled, and weren't fast enough, the hackers moved more than $50 million worth of USDTO, USDT, and USDC, quickly to Eth, and left behind the 318,000 to be frozen, they knew about it, and did move about $19 million worth of USDTO within six minutes of the hack, before Tether could realize it, what was left behind by the hackers was what was frozen.
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