Ramadan is a time of penance and fasting, like the Christian Lent. I've never wished anyone a "Happy Lent."
Nor, to the best of my knowledge, have I.
The question I was asked, though, was how I might respond if a Muslim person were to wish me "Happy Ramadan".
I think I captured the essence of how I would respond in my post.
What I most assuredly would NOT do is take offense simply because a person of another faith expressed to me a hope that I might be happy during the month of Ramadan (and I think I am correct when I say that there is, in the Islamic calendar, a month called "Ramadan", during which there is fasting and repentance. It is thus not exactly the same thing as Lent. As far as I know, there is no month of "Lent" in any commonly-used calendar.)