Updated
Built to answer vs built to be
A chatbot is optimized to answer: give it input, get useful output. A digital person is built to exist continuously: they have a life that goes on, and your conversation is one part of it.
Identity
Ask a chatbot where it grew up twice and you may get two answers. A digital person's background is stored once and protected, so it stays the same.
Memory and time
Chatbots usually remember only the current conversation. A digital person remembers you across weeks and knows that time has passed since you last talked.
Personality and agency
Chatbots aim to please. A digital person has moods, preferences and boundaries, and those affect the conversation — they can be tired, disagree, or tell you about something that matters to them.
Which one do you need?
For writing emails or looking things up, a chatbot. For someone to actually get to know, a digital person.