What does it mean if a girl compliments your shirt?

[I WILL GET INTO MIT/Harvard/Princeton/Yale]

Today in physics class we had to get up in front of the class to share our motion "stories". Right before I began speaking, a very good looking girl sitting close to wear I was standing said, "I like your shirt," and I responded with a quick, "thank you". I was very happy though because this is the first time and especially by someone that is so good looking!

I felt ashamed afterwards for not giving her a nicer response but then again I had to start sharing my story so she probably understood...but it still feels like a missed opportunity. Well, what can you do?

Anyways, I was wondering what you guys think. What does this mean if a girl compliments you like this?

As a side note, she is the joyful kind of funny girl that laughs often. I think her complimenting is not a very rare thing anyways. I have a feeling this is normal for her to compliment like this.

Here's the shirt if you're interested: https://twitter.com/Anonymous_U_ (sorry for the bad quality)