All transactions can be tracked and can be found on a blockchain. Depending on which cryptocurrency you are using, you can use the associated blockchain explorer to search for every transaction. You can search using a wallet address, hash, transaction ID etc…
So, if someone sends ETH from a brokerage account to an ETH address, you can find that transaction by searching for the wallet address that the funds were sent to via an Ethereum blockchain explorer. You can see a time-stamp and the amount of ETH that was sent, among other things.
Due to the nature of how the blockchain works, most cryptocurrencies are set up in a way that makes reversing transfers impossible. Think of it like an email. You can send an email, but once it’s sent, there’s nothing you can do to reverse it because there is no control over it once it leaves your computer. Likewise, you cannot force someone to send an email back to you and if you send the email to the wrong address, it may be lost forever.
Most cryptocurrencies are decentralized and autonomous and are not controlled by a single entity, so there is no, one source that can just stop or reverse the transfer. GUSD, on the other hand, is controlled and has been set up to be regulated, which goes against the very idea of what cryptocurrency was created for.
I will add to the point regarding the fellow that left his crypto sitting. It is never a good idea to leave your crypto sitting on an exchange or in your brokerage account. Always take precautions and be prepared for the worst. Always use a very strong username and password, and never use the same information for multiple accounts. I like to use a random password generator, e.g.:
https://passwordsgenerator.net/
If you keep a document containing your various login credentials, make sure to encrypt it by archiving it inside of a zip file or similar, and password-protect it using something strong, that you will not forget, but that does not contain personal information such as SS#, address, DOB etc… In fact, the website above contains a long list of tips that you can use to protect your data.