“He's a lot shorter in person.”
You saw a famous actor at a restaurant. You're telling your friend about it. You were surprised to see that the actor was shorter than you thought. You say this.
He's a lot shorter in person.
The meaning of "a lot" is similar to "very". But you can't use "very" with comparisons. For example, you can't say that someone is "very shorter" than someone else. When you want to compare things, you can use "a lot":
He's very short.
He's a lot shorter than his brother.
To see someone "in person" means to see them directly, when you are both in the same place. When you know someone from seeing them on TV, talking to them on the telephone, etc., you get ideas about that person. After you meet them in person, you can compare the ideas you had about a person with reality with the phrases "more ___ in person" or "___er in person":
Bethany is a lot quieter in person than she is over the phone.
He's more intense in person than I imagined.