bitcoin repo sighash.json data format
You decode them in exactly the same way that you decode a transaction. They are perfectly valid transactions and a decoder should be able to decode them properly and get meaningful data out of them. The reason they look weird is because every part of the transaction is randomly generated so the fields do not necessarily contain data that you expect (e.g. the version number is randomly generated instead of the standard 01000000 or 02000000).