Something is definitely wrong here. Code 1 indicates a distribution from his own retirement account, not a distribution from an inherited account. A distribution from an inherited account would have code 4. Does this Form 1099-R have the IRA/SEP/SIMPLE box marked?
I assume that your son's aunt died in 2023. Did your son receive a 2023 Form 1099-R related to this inherited 401(k)? Is so, what is the code in box 7 of that form. Normally a 401(k) would make a direct rollover to an inherited IRA, reported on a 2023 Form 1099-R with codes 4 and G in box 7 and the IRA/SEP/SIMPLE box not marked.
