Gosh that's a scintillating production shot!
I would assume that's during "Lazy Afternoon," as Helen and Paris grow closer/seduce each other in preparation for their elopement. The original production featured a shirtless Paris for a majority of the show and it seems that the Lyric Stage production followed suit.
It's great to hear how much you've enjoyed the recording CATSNYrevival, I hope that the new album makes many new fans of the piece!
Keeping BroadwayWorld Illustrated