Yugi shot Yami a look at that - This was serious, and he's laughing it away! But then he turned back to his grandpa, suddenly on the spot. A fire destroying Yami's home was absolutely dramatic! But he was right. His mother did love the dramatic things. She does love to watch soap operas, after all...

"... His house got robbed, he tried to catch the thief, but a fire broke lose in the house, and then an avalanche buried it and made him lose his memories?"

Maybe all of their suggestions in one explanation would work. Or just sound silly.