Job interviews are nervewracking. The stakes are high with what could be the applicant's dreams and livelihood on the line. It takes a real special ("special" meaning "entitled" person) not to take a job interview seriously.
People who have sat on the other side of interviews shared stories of the most bonkers things they've seen applicants do that totally tanked their candidacy. A benefit of tanking an interview this badly is that you're not left in suspense over whether or not you got the job. If you spent the interview texting, it's safe to say that their people won't call your people.