Ok...
So due to confidentiality (which doesn't apply to every bit of work stuff in reality but presuming it did):
Is it 'work' if you're in a private hotel room when answering emails?
What if one's spouse is taking a shower in hotel room, at same time? Coz spouse accompanied the non-worker to a work conference. But spouse might spot the screen -- so no confidentiality = no work.
What about meeting a potential client in the bar after evening meal at conference; you wouldn't socialise with them but they might be lucrative customer. Spouse comes along. Is this 'work' since spouse & the bar crowd are there to violate confidentiality -- I guess not.
What about a private workpod space in an airport? Can work be done there?
What about reading a scientific published paper while seated on airplane to learn some methods from it. Published info, but I guess that moment can't count as work since the activity isn't entirely confidential.
What if OP is the ONLY one in her train carriage (commuting home at 10pm at night). The guard will pop in -- so that can't be confidential.
If someone is working at home but a child wanders in where they can see the screen, or husband pops head 'round the door to ask where the car keys -- that entire day no longer counts as work coz you know, confidentiality was violated. Maintaining confidentiality is the only thing that matters in terms of calling it 'work' (I hear people saying).
I'm not even sure that working in my workspace counts as confidential, coz frankly, we are crowded in like sardines, and people on all sorts of pay grades could lean over or wander by & see my screen & info on there (violating confidentiality). Those people may be visitors to our office, not employees at all. The window repair guy, the building maintenance manager, clients. So it turns out, I'm not doing work even when I am in the office. I wonder if my employer knows...