I made a good answer with many methods to do one thing, and it had more than 80 votes, however there are a few AskUbuntu users that answered better methods and had only a few votes. I quoted it's answers on mine and said that the autor was "foo". Is that correct?
Is a good practice to quote another answers on mine?
No, I wouldn't say it is.
There are answers which work well in tandem, by being based on another, or complementing another. However, these are rare - most answers are independent of others.
It is true that people sometimes only look at the top (upvoted or accepted) answer, and not at other answers. However, it feels ... unethical ... to "profit" from another answer. If you do wish to include a selection of other great answers (with proper attribution, of course), I'd suggest making your post a community wiki.
Personally, I would never deliberately incorporate the content of another answer into mine.
As mentioned by Mateo, there is no reason to at all: the answer already exists on the question. An answer being accepted means OP found it most usefull for him or her, while another answer might be valued best by someone else.
Being accepted by OP is also no reason whatsoever that the answer should be the "universal" one, covering all other answers. The link you include does not prevent the fact that it is borrowed, duplicated content.