Maybe he bubble wrapped it and tugged the monitor with towels and clothes in a luggage firmly in place and well cushioned. I have once carried an Acer 20" monitor and small form factor PC in a Check-in luggage while returning from Singapore. Used bubble wrap and towels for cushioning the equipment very carefully.
Yes. The biggest allowed suitcase size can fit a 24" monitor with its thermocol (the one you get inside its box). That's what my friend informed me. Then put clothes above & below it. Surely occupies a lot of space.