That's pretty funny. Grandparents definately have a great sense of humor. He was probably entertained by your reaction too.
One story my late grandfather told me about was from the 1960s. He was an engineer who owned a pool construction company from the San Francisco Bay area. His company built the swimming pool for the Olympics in Mexico in 1968. He chartered a DC3 to fly some of his crew and supplies down to Mexico City from SF. Somewhere in Baja they had engine trouble...in his words "the damn thing was on fire and sprayed oil all over the place!". They landed at a nearby field that happened to have some other DC3s on the ground. He made a deal with the Mexicans that they would replace the engine on his airplane if they could borrow his rudder. I guess one of their airplanes had a damaged rudder and they wanted to use it. My grandfather assumed they would only use the rudder for as long as it took to replace the engine. The mexicans were gone for two weeks! For a week and a half his airplane sat on the ground with no rudder but two good engines. He laughs about it now but I'm sure he was more than a little steamed back then.