Why do Chinese "extend" the last word when speaking?
This kind of case is usually occurs on these occasions:


When you are standing at top of the mountain, you feel very exciting, and shout out with prolonging the each word(like niiiiiii haooooooo maaaaaaa) or just the last word(like ni hao maaaaaaa). Mum, so exciting! :p
It usually occurs in young people, especially the female. Some cute girls will often prolong the word in front of her boyfriend. 你好吗~~~(ni hao maaaa), 想我吗~~~(xiang wo maaaaaaa), etc. This is often described as 嗲(dia3) in Chinese. When chatting via Internet, ~/'/. characters will often used as the word prolonged.
Sometimes, wife will do like this in front of her husband. Just like the case No.2. :)


And for your last question: you did not misunderstand. :)