Why would he say thank you after I kissed his cheek?

So my childhood crush (he gave me a diamond bracelet when we were 11) and I reconnected after 10 years, we picked up right where we left off about a year ago now, it's as though there was no time in between. He is very shy and only had one girlfriend. Well I finally decided to give him a kiss on the cheek and he said "thank you" lol... I thought it was cute and sweet. Could he have just been nervous and didn't know what else to say? I mean he did call his buddy up one day last week cause I needed a boost and told him I owe him a kiss. Either way, it was so cute

Why would he say thank you after I kissed his cheek?
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