Earlier quoted context omitted.
The form of an argument is the opposite of semantics. If someone made an argument like "Korean has an independent origin from Chinese. You might doubt it, but what evidence do you have that it's not true? If we don't know that it's not true..." then that would be argument from ignorance, as well: notice how no supporting evidence is mustered for the hypothesis.
P1: "Korean has an independent origin from Chinese." P2: "I don't believe this is true" (because my background assumption is that things originate from China) P1: "What evidence do you have that Korean isn't independent of Chinese" P2: "None, we have no evidence from this time period." P1: "Therefore, Korean has an independent origin from Chinese." P2: "That is argument from ignorance." P1: "Here are differences betw…
Where P1 offers some discussion of differences between Korean and Chinese, that's where we start to get into a discussion based on evidence that can be evaluated. If P2 doesn't find it convincing, then we can ask why; this allows P2 to muster evidence which can be evaluated. That's a fine and constructive direction. A finite conversation like that doesn't necessarily end with a solid conclusion and everyone being convinced of the same thing.
What you're pointing out with regards to the perceived strength or weakness of certain assumptions is not what we're talking about with argument from ignorance: argument from ignorance is about the form, not the semantics.