Question 1 in these contexts is effectively a "proper noun" (it identifies one specific thing).
For the same reason why we don't refer to the1 OP as the Riko, we don't use a definite article when referencing Question 1.
1 Note that OP normally stands for Original Poster (the person who originally posted the question). Sometimes it's Original Post (the question itself), but I don't usually use it in that sense myself.
In this particular context, it's a matter of intended nuance whether to include the before OP. It depends on whether the writer is thinking "locally". Within the context of a single question, OP identifies a single individual (so in this case, OP corresponds to the one-and-only Riko, and doesn't require an article).
But if the writer is thinking in broader terms (where OP more "generically" references anyone who posts a question), the definite article is required, as he's talking about a specific OP (this one, Riko).