KISSSSS...was it GOOD or BAD? WHAT DID HE MEAN BY THE WAY HE RESPONDED?

i kissed him on the cheek & he said "oh" in a soft tone while quickly exhaling, not in a whiny tone but perhaps slightly surprised "oh" when my lips were against his cheek & then said "thank you" when i was done....SO, why would he say anything? what did it mean?