They just introduced the letter غ /ghayn. They have to combine it with letters we already know to come up with easy words with which we can practice the new sound. غريب is a word they chose. My paperback dictionary lists the meaning as: strange, odd, peculiar, foreign, stranger, and foreigner. People say "that's weird" or "that's strange" all the time. It'd be weird if they didn't.
They are very different, Ghayn can be seen s a G in the back of the throat, like gargling. Ayn (written as 3 in latin alphabet) is more of a force in the throat to stress a vowel (press air out of your throat while saying the letter A for instance, in uni my arabic teacher always told us ''You aren't doing it right until you find yourself sounding a bit ridiculous'' (no offense to native arabic speakers obviously)
Thank you, rickkorst and ErezGavish for your help with ghayn. May I ask you about another difficult consonant in Arabic? Some authorities say ق is voiceless, and some say voiced. I had assumed it must be voiceless, since it had been presented as comparable to ك . What do you say?