Right?? It's a love corner not a triangle Love triangle = dajeong → haneul → XLove corner = dajeong → haneul ← X AA hon
The classic love triangle is one person torn between two people. So while you're right this doesn't look like a love triangle (because neither Haneul nor Dajeong would reciprocate), your definition is also incomplete
a third party having a crush on one of the mcs ≠ love triangle
omg lighten up ppl this is just to create some jealousy and to keep the plot going