"Topped" is spelled with two p's. English spelling is crazy and there are no reliable pronunciation rules, but this spelling tells a native English speaker that the "o" is a short "o," as in the words "top," "hop," and "pop." "Toped" is pronounced with a long "o," as in "tope," "hope," and "Pope." "Toped" is a very, very rare word. Since it is a real word, a spelling checker will not mark it as wrong. That is probably why the spelling error was not corrected.
To "top" something can mean "to put, or to have, something on top." A mountain can be "snow-topped." It is usually used with material that is spread out in a thin layer. It is used most often in connection with food, as in your example Ice cream can be topped with chocolate sauce. Pizza can be topped with pepperoni. The material that goes on top can be called "a topping." Pepperoni is a popular pizza topping.