Schengen has independent of the EU status. Eg. you can move freely from Germany to Switzerland (without obligatory border check) but not between Germany and EU-member Cyprus (there is the obligatory border check).
EEA gives you that, and Iceland is a member state of that too. So Iceland already enjoys this freedom.
I think Switzerland has a bilateral agreement with the EU (or via EFTA) that allows for free movement and employment of people, so they enjoy these freedom as well despite neither being in the EU nor the EEA (but they are a member of EFTA).
Yeah, I don’t know about what is included in the bilateral agreement with Switzerland. But at least in EEA (which is EU + EFTA - Switzerland) you are free to work in any of the member states.
The person you are replying said "moving" as in you relocate to another country. Not going on vacation. Swiss people can not just move to say denmark one day and start working there. They need work visas etc for that.
Switzerland is both a member of Schengen (meaning no border checks) and its nationals enjoy FoM (via bilateral arrangements). They don't need work visas.