The link you provided does give the answer to that question:
il s'agit de (=c'est) - it's a matter of, it's
(=c'est à propos de) it's about
Il s'agit d'une intervention bénigne. - It's a minor operation.
de quoi s'agit-il? - What is it about?
So, there you have a translation, a proper question and an example.
Un francophone also provided il est question de and that can be also said in English: it's a question of.
Il s'agit d'une pièce à deux personnages. - It's a play with two people.
With own words: You can use that phrase when you want to specify the object you're talking about more precisely. For instance: It's an animal with eight feet.
Thus, your sentence could be translate:
It's indeed Drago Malefoy.
Admittedly, it's Drago Malefoy.
Said that, I wouldn't use a question of or a matter of in your example. Both could be used in the second meaning that Un francophone said, for instance:
It's a matter of life and death.
It's still a matter of debate.
or in phrases like
It's simply a question of time. (C'est juste une question de temps)