The author clearly doesn't know what they're talking about and doesn't have a mind for the law or for safety in general. Being in a separate building and watching a monitor is not safe. This doesn't allow for monitoring of unsafe conditions such as fires, nor is the reaction time reasonable for things like if they climb out of their crib or get out of bed (if they aren't an actual baby). The person should be on the same property. Depending on jurisdiction? There will be legal problems if they aren't.
Does same property really guarantee safety? I have 5 acres and so could easily be on my property but much farther away than a neighbour in a more condensed neighbourhood.
What if someone was in an apartment building and “next door” was the other side of a shared wall?
Most of the laws refence being attended by an adult or being in line of sight. It's most likely that the authorities would charge you in either example you gave.
