I looked around a bit, and I find no way the old account is connected with requestor's off-wiki identity. There is no email attached, enwiki userpage has no off-wiki information. Not sure if the user is reading the ticket, but do they have any way to prove the relationship between the two accounts?
They commented on WP:CHUU, ''I had an email attached to it, the same email as for my current account and I removed it and a bit after I changed the password, but did not write it down. So, I could not get back to my account the next time I tried to login and had no email to recover it. BTW, in the archive of my mail client, I have records of emails that I received under my previous account. Would that be useful? Dominic Mayers (talk) 13:58, 11 May 2021 (UTC)''
If possible, check if email attached to old account was same as current one?