[Fran~]

Exactly... to Mugi, Yui, Ritsu and Miu are mere commoners... so to her, this is like a field trip, or a safari.

Remember how Tamaki was amazed by Haruhi's appartment... this is the same with Mugi. Probably the attitudes of the girls are also the first time she sees a girl who blushes from everything, or a teacher like Sawa-chan.

I can bet that a lot of people who see this anime put the same faces than Mugi... and i dont think that those persons are putting this in a "sexual dimension".