Jinwoon is well known for searching his name and responding to tweets. Mostly, the replies don't really get the attention of others except the one he responded to, but a recent response has everyone retweeting.
A netizen wondered, "Which group is Jinwoon from again?" on their Twitter, and Jinwoon graciously responded, "TWICE". When netizens saw the tweet, they couldn't help but laugh, and TWICE fans happily welcomed him into the group.
You can see the thread (and responses) here.