What kind of person makes such a transaction?
Its important to understand how bitcoin transactions work here. Whoever spent that output didn’t necessarily send 300 BTC to someone else!
Under the hood, BTC exist as ‘unspent transaction outputs’ (UTXOs). Each UTXO has a certain value (the number of bitcoin it represents), for example someone may own a 300 BTC UTXO. To spend any amount of that money, the entire UTXO is consumed as input to a transaction, and new transaction outputs (UTXOs) will be created at the same time.
So if you owned a 300 BTC UTXO, and wanted to send someone 1 BTC, the transaction might look like this (ignoring transaction fees):
Inputs: (300 BTC) --> Outputs: (1 BTC) (299 BTC)
Of course, it is also possible that someone really did spend 300 BTC all in one go. Or it is possible that those BTC were just transferred between two addresses that are owned by the same user. Or maybe multiple people were paid at the same time! Without being party to the transaction in question, its tough to say much more for certain.