It's not lying by omission if the contributor didn't want it mentioned. Or he's done minuscule extra work. Or it was years ago whilst he was a student. Or the 'whistleblower' has an axe to grind.
Look, I didn't work on the programme so can't answer on the specifics involved but I stand by my previous comment, in 20 years of working in telly I've not - nor have I worked with anyone who has - knowingly tried to pull the wool over viewers eyes. I've never ever heard anyone sat "feck it, don't tell the truth - they'll never know!"! The exact opposite is in fact the case; "Did that happen, is that an edit, can we substantiate that, have the lawyers signed it off etc..."
Unbelievably, we want you to enjoy the programmes made! Be entertained! We don't want to shoot ourselves in the foot by knowingly deceiving. As an individual, one would never get employed again - regardless of what it'd do to a production company.