I'd say that the issue the author is addressing is that it is not so overt. Sure, if you meditate on it it becomes clear it's a subsidy, but I think the vast majority of the people who take advantage of it simply think "I produce as much as a use, so of course my bill should be zero."
The straightforward solution would be to fund major infrastructure costs using something other than volumetric pricing. But it’s easier to just impose fees on solar.
If you're using a generator (or, as another comment said, just use hardly any electricity) then you're not a burden on the system at all (or barely).
If you're "net zero" because you feed the grid your excess power during the day and take away power during the night, you're using all their infrastructure.
In your example, you don't need the grid, so it makes sense not to pay grid overhead (minus arguments about how we still pay for schools with taxes even if we're not using them).
In the solar example you absolutely need the grid. So net metering down to zero is definitely a subsidy. A subsidy I absolutely agree with, but a subsidy none-the-less.