You're 100% correct. At my current (and next) job, I'm required to be on call 24/7/365. If there's an outage of some sort, I need to be able to help fix it or organize the people who can fix it. Being down for an hour while doing yoga could cost the company millions. The person who sounds self-absorbed in all of this is the instructor -- "It's only Facebook, not talking about Russia bombing us." She obviously has no concept of business and I would counter that SHE'S self-absorbed thinking the world needs to revolve around her class. The business needs to go on; I doubt the employee was simply surfing the web at the time.
Again, I'd counter that in this case, it wasn't a laziness issue -- it was a business issue. I doubt she was checking her Facebook status or tweeting about her class. I'd agree that smartphones have become digital leashes on employees -- mine's sitting in front of me right now in case of an issue at work -- but that's the opposite of lazy.