And it's not the hack itself. Crypto projects get hacked every week. Multichain bridges are the target of the month, with eye-watering amounts and complex code running on different blockchains, and off blockchain. And a Solana bug like this one is to be expected.
What is surprising is to see a project promise to fully repay everyone, within two hours of the attack occurring. That size of cash for a "we'll fund it back up", and that kind of speed is really unusual.
In the immediate aftermath of the hack, people were commenting that the now unbacked Solana side eth was still trading near its normal prices, and it stayed that way until the announcement. This leads me to guess that insiders must have known that there would be a chunk of money coming to refill the coffers after the hack, which in turn means that the decision to send the project hundreds of millions of dollars must have been made at or before minutes had elapsed from the hack.