Is it considered a lie if someone gives charity from their own money and says, "This is a charity from a person," when they mean themselves?

It is permissible to resort to tawriyah (double entendre) and ma'arid (euphemisms), which are phrases from which the listener understands something different from what the speaker intends. There is no religious fault in this, as long as it does not lead to upholding falsehood or nullifying truth. Therefore, your statement "This charity is from a person" is not considered a lie if you intended the listener to understand someone else, while you meant yourself. Lying is informing about something contrary to reality, and it is forbidden.