I think the app can not recognize if that account is real people or scammer because they can buy any number from their country and use it to scam any people in that group. People will only know the number and name of that person, but they do not know if that is real people who want to interact with other people in telegram or scam people. The best way to prevent scammers or fake accounts is by deleting the conversation they start or reporting it so they can not message you anymore.