Tony, they could be right. About you not liking it, not about you being a stupid foreigner. It's a bit of an acquired taste. Horta is basically boiled greens, so there's a few varieties to go at and what you get can depend on the time of year. One variety - vlita - is also known (although probably not in Greece) as
Guernsey pigweed. Enjoy!
BTW - kokoretsi is delicious!
Whichever you try... I'd have a large ouzo standing by