Sometimes the sounds in the duo practice is wrong but their dictionary sounds good. When I think something sounds off I just type it in the duo dictionary to get the accurate sound. The correct sound for rajul is here https://www.duolingo.com/dictionary/Arabic/%D8%B1%D9%8E%D8%AC%D9%8F%D9%84/b24245eb676b547b58a56d7b632ae6c5 Hope it helps.
They are the same (for me), in your link or in the audio button above. And it is correct anyway, but with a minor mishap here in this sentence. Since the word (rajul) is in the beginning of the sentence and there is a word afterward, the ending vowel must be added (something that dialects don't do). So, the proper way to say this sentence would be: rajulun lubnániy.