Should I expose a couple playing a dirty trick to avoid paying their restaurant bill?

Should I have revealed the truth?

In a restaurant recently, I noticed a young couple on the next table pull off something that was clearly unethical. Towards the end of a lavish meal, complete with wine and cocktails, the lady quietly pulled out a dead insect from her bag and dumped it on her plate. They created a huge ruckus thereafter, insisting that they wouldn’t pay the bill. Should I have revealed the truth?