> you've obscured the fact that the function is periodic
No. Periodicity is not a property in a graph. The graph still shows the function in that domain neutrally, as far as I can tell. Neutral meaning: impartial, without strongly marked characteristics.
If you insist on periodicity: there's an infinite (uncountable) number of properties not shown. If that violates neutrality, every statement is biased, which makes the article's statement rather trivial.
If you have to specify everything in text and you don't intend to actually communicate anything through graphics and if you only focus on pure, sterile mathematical functions which don't have an ideological component that could be biased to begin with... then surely you can see that your statement is the trivial one.
> The graph still shows the function in that domain neutrally
The key word being "in that domain". You can use the same excuse every time you mislead people with statistics. The fact that your choices can mislead people proves that they're not neutral.
You have to accept the limitations. A map is not the territory. Everyone knows that and accepts the map for what it is (because it is useful). It is not misleading to present a graph in a limited domain. It conveys that it does not represent the full function.
But that's not what neutrality is about. Being neutral does not mean representing the full truth. It means: not distorting, being impartial, not stressing a particular aspect, etc.
Assigning neutrality or bias without viewer of interaction is a category error. It is not an intrinsic property of the graph despite our wanting to simplify the world this way. It's like saying chocolate is intrinsically the best candy when what's being said is 'my relationship to chocolate is that it's my favorite.'