For years now, many have come to know this position as doggystyle but recent internet fiends would use backshots instead, likely because it's a little fresher and less stale. Information and translations of backshots in the most comprehensive dictionary definitions resource on the web. It is indeed a “sex joke”, yes
The magic of interracial backshots with a BBC : BackshotsFromBBC
“backshots” refer to one partner being penetrated from behind
The joke is in the possible double meaning of the poster’s original comment, which he quickly realises (or intended all along).
Receiving a force of feeling/damage from someone else while they're on another back. ‘backshots’ is an unabashedly vulgar slang term referring to sexual intercourse from the rear position, typically meaning the penetrative partner is positioned behind their consenting cohort Backshot is a slang term that originated in urban communities to refer to a sexual position where the male partner penetrates the female partner from behind The term stems from the act of delivering a strong and forceful thrust during intercourse, often resulting in intense pleasure for both parties involved.
Definition of backshots in the definitions.net dictionary