To be honest I'm not really sure. I can only presume they are implying they are on the same exchange. I've only just noticed that particular turn of phrase in the last four to six weeks perhaps.  A lender only has to start a scam accusation and a genuine borrower will go to any length to prove they had made the repayment.

I haven't been registered on an exchange since Cryptopia and rarely swap coins via instant exchanges so I'm very unfamiliar with the procedures modern exchanges use for internal or external transfers.

I'm also startled to read a major exchange might somehow be using a single hot wallet for both incoming and outbound transactions. Given that exchange has suffered hacks totalling in the millions of dollars dating back as far as 2017, I'm surprised the Exchange is still trading at all.