no error or glitch, USCIS is on fire to approve AOS without interview especially ( not all) for people who just got married or before 2 years anniversary of their wedding. dont know the reason why, but my guess, they want to bank in the money for the next step when you guys filed for Removal of COndition. there's no hard rule who got interview waived or not. i think it just depend on the officer. congrats ! and card usually will come within 1-2 weeks.