Actually, this is part of the things that characterize Islam as a religion of peace, a religion that calls for showing fellow-feeling, love and affection to our brothers, Muslims and non-Muslims, for Islam caters for the well-being of all creatures, not only human beings.
Therefore, upon this basis, Muslims are allowed to share their happiness with others. But Ramadan is a special month for Muslims, Suhur (pre-dawn meal) and Iftar (fast-breaking meal) are special occasions for Muslims in Ramadan, in addition to `Eidul Fitr (Lesser Bairam) that stands as part of reward for Muslims for spending the whole month in fasting. So Ramadan as a whole is a special occasion for Muslims. But this does not mean that the occasion is to be spent in isolation, away from other people, non-Muslims.
Shedding more light on this issue, we’d like to cite for you the fatwa issued by the eminent Muslim scholar, Dr. `Abdul-Fattah `Ashoor, Professor of the Exegesis of the Qur’an at Al-Azhar Univ.:

Iftar comes after observing fasting, and we know that non-Muslims do not observe fasting. That’s clear. But if conducting Iftar for non-Muslims is meant to strengthen the relation between Muslims and non-Muslims, it is permissible. Allah says, (This day are (all) good things made lawful for you. The food of those who have received the Scripture is lawfu
l for you, and your food is lawful for them.
(Al-Ma’idah 5: 5)
no doubt, such thing can help non-Muslims understand the true Islam and know that Islam is the religion of tolerance, peace, and brotherhood. Allah says in the Qur’an, (Allah forbiddeth you not those who warred not against you on account of religion and drove you not out from your homes, that ye should show them kindness and deal justly with them. Lo! Allah loveth the just dealers. Allah forbiddeth you only those who warred against you on account of religion and have driven you out from your homes and helped to drive you out, that ye make friends of them. Whosoever maketh friends of them (All) such are wrong doers.)(Al-Mumtahinah 60: 8-9)
Besides, Islam was not spread by force; but it was spread by means of intermingling with non-Muslims. Thus, Muslims, in their dealings with others, should appear like the sun that shines and melts away darkness.