Terry Unmarried was 2APS17. This episode was 1APS15. Meaning it was made a year ago way before they thought of the "Terry's gay" plotline, but didn't get aired until now.
They'll probably revisit the plotline in future episodes. This week's Family Guy had Cheryl Tiegs, which Quagmire mentioned in an earlier season. As much retconning it gets, sometimes the "Seth-verse" has a continuity.