New hire shows up to his first day at the office, only one employee notices he's not the person they interviewed : 'No one else seems to notice that it's a completely different guy'

Interviewing is so different when it's done over Zoom. As an interviewee, you can have a Google Doc open with all of your stock interview answers (and the answers specific to this job) written down so you can read them right off the page. It will be obvious you're doing this if you're an amateur, but the level of detail you can go into if you're not just working from memory is hugely advantageous. Even though many recruiters prefer meeting someone in person to gauge their IRL vibe, the convenience of hiring anyone in the world, no matter where they live, is more valuable to some companies than having someone who is fun to talk to at the office. 

Sometimes, not meeting a new hire in person can backfire. In the case of the company at the center of this story, you could interview one person for a position, and a completely different guy could show up when his first day of work came.