Guy's Behavior

Why’d he respond like this when I asked his number?

I’ve known and worked with this guy about 4 months and I’ve considered us friends for the majority of this time. We have communicated outside of work only through social media. We joke around and play fight from time to time and have a ton in common. I’ve wanted him to ask for my number or give it to him for sooo long, but felt weird asking for it without being obvious. He told me to send him something the other day and I said well give me your number, and he was like “Oooooh” in a high pitched voice like it was a big deal. Like he might as well have said “oh I knew you liked me.”

I think he likes me for a lot of other reasons and he already knows I like him. We flirt a lot as well in different ways, and I felt like it was weird us being so close at work and not having one another’s number especially being friends and having hung out outside of work. It felt like a question hanging over us for a long time. But I wasn’t expecting that response from him.
Why’d he respond like this when I asked his number?
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