Should I flag it as a duplicate question, even though the parent of that answer is not the same language, or is some other flag more appropriate, or some other action the best?
No, they're not duplicate questions.
Answers are not considered when evaluating questions as duplicates, and in this specific instance, the questions only bear a passing resemblance.
Your link is correct and does answer the question. I did flag that this question myself as a duplicate (though a duplicate to a different question than you did). I linked to another for the same language that the OP was asking about, but the ultimate response is the same.
I don't think it matters so much; if it is a duplicate problem and/or scenario with a duplicate answer, even with some a few differences, it's a duplicate.
Because there's been previous frowning upon removing C# tags for general .NET questions asked by C# users, almost all C# questions can be asked again as VB.NET (and F# and C++/CLI) questions.
But in this case they're clearly not the same Question, so no, these are not the duplicates you're looking for. (Clearly there is another duplicate question to point to.)