As macuser_22 indicated, your distribution is from the designated Roth account in a qualified retirement plan like a 401(k), not from a Roth IRA.
This distribution will appear of Form 1040 lines 5a and 5b as a pension or annuity. Any Form 1099-R that is not from an a traditional IRA (IRA/SEP/SIMPLE box marked) or a Roth IRA (code J, T or Q in box 7) is reported as pension or annuity income. In this case, the code B indicates that this Roth account is not a Roth IRA.
