“was caught” is a passive voice expression meaning “was caught,” formed from the structure Verb to be + Past Participle (V.3).
The idiom “catch someone doing something” is used when you accidentally catch someone doing something (often something bad or secret) or when you catch them red-handed.
This type of message often uses clickbait, where the sentence is cut short before the key word (in this case, “sex”) followed by “See more” to pique the user’s curiosity and encourage them to click and read further on social media.