What I mean is workers who leave for lunch are more likely to come back later. Coming back late from lunch happens all the time and no one is fired from Accounting for taking 45 minutes instead of 30 minutes.

Workers taking lunch with other workers in the office are also more likely to talk about work as compared to meeting friends outside of work for lunch. If you are talking about work during lunch with coworkers, that's like having an office meeting during lunch.