If you inherited the IRA from your spouse and assumed ownership of it, the Uniform Table is used. But you cannot be treated as the owner of the inherited 401k and if you leave the inherited 401k in place, the single life table applies which produces a much larger RMD as % of account balance. If you are the surviving spouse you can do a direct rollover of the inherited IRA to your own IRA, and then the Uniform Table will apply.
There are also other possible explanations. Are you the sole beneficiary of the 401k, and has the plan indicated that the “actuarial life expectancy” they refer to is derived from the Single Life table?