How exact is a numeric requirement in a commercial context? It's mostly a matter of convention. Here are some examples:

A real estate agent describes a 392 square meter house as 400 square meters. Is that close enough to correct? For most people, yes. But I know someone who filed a lawsuit over a similarly small misstatement. Perhaps that person would be at home working for RyanAir.

A speed camera tickets you for driving 56 mph in a 55 mph zone. Reasonable? Most people would say not. A judge would probably uphold the ticket, but that decision would not be popular. People are accustomed to some leeway on speed.

You offer a car for sale on the Internet saying it has 120,000 miles. It actually has 120,384 miles. Have you committed fraud?

It's always a question of reasonableness. Is the departure from the stated number reasonably small or not? RyanAir does not appear to conform with customer expectations of reasonable enforcement of its limits.

Scientists use either significant digits or stated tolerances to define how much error is acceptable. Lawyers apparently don't.

I think I'll bring a tape measure to check RyanAir's sizing box and make sure it's the proper size. Turnabout is fair play. @:-)