my heart's a stone I'm throwing at your window

"Harry grew up in the Muggle world. Even if he did find out that magic was a real thing only six years ago, he had adapted pretty nicely to the notion. So why would it be so hard to believe the fact that a sixteen-year-old dragon (who went to a Muggle school, apparently) just told him (in an American accent) his zodiac sign?" (Set during Half-Blood Prince, slight AU for AD:JL)