Unless the Form 1099-R is erroneous, the code 4G Form 1099-R indicates that you did not inherit a Roth IRA.  It indicates that the distribution that you rolled over to a Roth IRA was a distribution from a traditional account in the qualified retirement plan, not from any kind of Roth account.  Such a rollover is generally taxable.  The taxable amount will be shown in box 2a and any nontaxable amount will be shown in box 5.