Or is it that they needed income statement for your electrum account to satisfy your KYC requirements? If it's that then it's not a big deal and it's just for you to go print out your electrum wallet statement to satisfy that, tho I haven't gone through such processes before to give full details on how it should go but you need to be careful with such tho.
Printing out his statement from his Electrum wallet is not a big deal. There is a thread in this forum that discusses how to print out his transactions from blockchair.com.
How to generate a Bitcoin Statement of Transaction. It might be helpful to OP if that's what the casino really needs. As much as they didn't ask for other private information like wallet passwords, passphrases or seed phrases, transaction statements pose no harm.