Nostalrius Begins - Quality wow vanilla realm (1.12)

Hi, i played on many vanilla servers but haven't played on retail. I have a question about mage's Detect Magic spell. I know that warlocks' curses can be used to dispell effect of Grounding Totem. The question is why Detect Magic didn't has the same effect?

Grounding totem absorbs a harmful hostile spell. Detect magic is hostile, but not harmful