Mistakenly means as the result of being wrong about something. Mistakenly believed, mistakenly sent, widely but mistakenly.
It is the polite correction word, since saying something is mistakenly believed is gentler than calling it false. It says the error was honest, which is what separates it from deliberately.
1adverbmistakenlyAs the result of being wrong about something.
“Many people mistakenly believe that bats are blind.”
mistakenly is a manner.
From mistaken + -ly.
Etymology from Wiktionary, CC BY-SA