Yeshivish is a style and mode of dress speech and lifestyle. Its an external way of looking or acting which may say something about te yeshivah the boy attended and the family he is from. It doesn’t necessarily mean a person is strict in their observance. You can be yeshivish and watch movies follow sports and listen to non Jewish music and do lots worse…trust me I know I’ve attented yeshivish yeshivahs. Don’t judge a book by its cover. I know plenty “modern” looking people who put many not modern looking peoples davenings, learning, and middos to shame.
As Rav Gifter Zatzal says, we should strive to be Torah Jews.