It's part of his PR campaign. His political team and the PR firms he hired probably did a lot of research and polling and decided this was a great way to appeal to younger voters.

Politics is all about image and appeal. And it's not just Beto. Every politician from Trump to Beto plays this game. People vote on their image of you rather than who you really are. I think Black Mirror had a great episode on how image and messaging defines a political campaign.