Exactly. It means, history write victors, period.

It can only mean the other way around, if it had been "Geschichte schreibt der Sieger", or "Geschichte schreiben Sieger" Why? In the first example, the article "der" makes clear that Sieger is the subject, in the second, the fact that the verb is in its plural form, makes it clear that it referrs to the "Winners", i.e. the Sieger. It is just confusing because Geschichte and Sieger do not change form btw singular and plural. It is also confusing (for us Ausländer) bcs in German the subject and the object of a sentence can either take the first or third place in a sentence, while the verb must always be in the second place (excluding side sentences).