If OP sent the coins from a custodial wallet and the transaction was confirmed on the blockchain, can it be reversed?
Depends. If both users use the same exchange and they both own no keys, then it supposedly can be reversed, exchange-side.
True, but that's not an on-chain transaction. Centralized exchanges like Coinbase or Binance allow users to transfer "balances" from one account to the other, but those transactions don't move any bitcoins around. The bitcoins were and remain in the wallet of the centralized party, only balances sheets are changed and updated.
I have a more important detail about the OP's message:
a company called funds-recovery.com has said that we can make a claim
I think most likely the OP is shilling for what is likely a scam site funds-recovery[dot]com. No reputable business is going to say that electrum is liable in this case. It might be understandable for a frustrated user to want to blame someone else for their mistake, but there isn't anyone running a business trying to recover funds from electrum as the OP describes.
It doesn't necessarily have to be shilling for that site, but you are right, it could be. It could also be just a scam site he found that is looking to take advantage of people who lost money in an attempt to profit from their ignorance.