The use of gypsy as  a contra dance term is almost as  offensive as a contra dance containing a shadow swing. (JUST KIDDING)

I would suggest a response of the following nature:

Hello _______

As you noted,   (i)   you were  impressed by the friendliness of the dancers, the quality of the musicians, and the overall fun of the dance; and (ii)  this was probably the best first experience  Iyou had when meeting a new dance community.  

On the political spectrum, contra dancers on average are far to the left of center, with quite a few very far to the left.  They would not tolerate a term with intent of disparaging any group.
The term gypsy (walking around another dancer shoulder to shoulder) has been used in contra dancing  ever since the motion was introduced into contra dancing--probably several decades ago.    [Insert information about the origin of the use of gypsy from previous posts on this thread.]
Many words and expressions have origins long forgotten in the context of their current usage.  You can find many examples of such at  
http://www.mirror.co.uk/news/uk-news/words-literally-changed-meaning-through-2173079
In xx years of contra dancing, yours is the first lament about this word that I ever heard.   For contra dancers the word has no other meaning than walking around another shoulder to shoulder.

Our contra dance community takes great pride in the friendliness and fun of our dances
Hope to see you at our next dance.

Regards,
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Michael Fuerst      802 N Broadway      Urbana IL 61801      217 239 5844