I just started taking ear training lessons and my teacher was surprised that I can't hear 2 separate notes when they are played harmonically.I can hear that it's not a single note, but she can sing both of them. Am I in a small minority?
Your teacher shouldn't be surprised. It's not something many of us are born with. Like so many things, it can be learned, and is a good skill to have.
Your teacher could play two notes together, then split them. After a bit of experience, you should be able to listen to the blend and identify each separately. Think they may belong to a chord, or arpeggio. Try to differentiate between the lower and higher note. Discover intervals, and know what interval between two different notes sounds like. Get teacher to play just one note. you sing a M3, P5 et al after. Get to decide if it's 1, 2, 3 or 4 notes the teacher plays simultaneously. Have fun.
Your comment "I can hear it's not a single note" might indicate that there's hope for you. Actually, ear training is about learning to hear those notes and then learning their relationship to other notes. And it can go on and on from there to being able to identify pitches when you hear them. It's a skill that can be learned by most people if they study and practice. You might have reason to worry, if she couldn't do that because she's the teacher. She can probably teach you to do the same. Let her.
No, you're in the large majority group 'People who have only just started training their musical ear'. You will soon progress into the elite group: 'Musicians with developed aural skills'. Welcome!
After (most of) a lifetime spent with music, I still sometimes have trouble picking the notes out of a chord. But I usually get there in the end. Don't despair!