You don't have either a Saturday night or 7 day minimum stay in there and so this roundtrip doesn't qualify for cheaper roundtrip non-refundable fare offerings (it will only qualify for one-way fares for each direction of travel). Shifting departure to 11/29 qualifies for cheaper roundtrip fares which have both non-refundable and refundable fare variants. It seems all one-way fares on BOS-MUC are refundable fares and hence "Extra" fares. It looks to be an outlier as most other US markets to MUC (JFK-MUC, for example) look to have both non-refundable and refundable one-way fares.