Advertisers surely know he's full of crap, too. He can make up fake views, he could even have bots click on ads, but unless he's also going to fake being a customer it will all come out in metrics. Savvy advertisers track all of that. Clicks per display, sales per click.
I’m curious about what their definition of “engaged” is. I imagine most people don’t make comments on YouTube videos, but twitter’s main focus has always been posting and commenting on others’ posts.