First, it helps to STOP using all capital letters. That makes it hard to read.

Next, this is a discussion forum on the internet and full sentences with details really help with complex issues.

Something was converted; if that was not from one account that you know about, then he needs to tell you where the conversion came from. No one on the internet can answer that question. Did you ask for last year's paperwork? The 5498 for a 2021 conversion might be from a distribution 1099-R dated in 2020, such as, a rollover can have a delay.

You need to ask him about his retirement account activities.

Conversions are nearly always taxable unless, for instance, it is a nondeductible IRA contribution immediately converted to Roth, which means no earnings to tax, post-tax contribution converted, and there has to be no other IRA-type money that is non-basis. Otherwise, any conversion is pro-rated for taxes.