Read the ECG topographically. The triad of $II$, $III$ and $aVF$ defines the inferior territory of the left ventricle. The artery feeding this territory is the one that gives off the posterior descending branch.
Because the human coronary circulation is right-dominant in the large majority of individuals, the posterior descending artery is a branch of the right coronary artery. Hence inferior wall ischaemia maps to the RCA. The same vessel typically supplies the SA and AV nodes, which is why inferior MIs are classically associated with sinus bradycardia and second-degree AV block.
Contrast this with anterior changes ($V_1$-$V_4$, LAD), lateral changes ($I$, $aVL$, $V_5$-$V_6$, LCx) and the global ST depression with aVR elevation seen in left-main disease. None of these fit an isolated inferior pattern.
\[\boxed{\text{Inferior wall MI (II, III, aVF)} \rightarrow \text{Right Coronary Artery}}\]