The poster wasn't quoting a source because the information hasn't been neatly put in a "source" such as your source which has been neatly put together by a foundation with huge amounts of money and resources and time at their disposal who are seeking to illustrate that their pro immigration idealogy is cogent. The poster was instead saying that anyone who looks at the statistics and uses critical or independent thought will see the problem, but that no one has yet compiled the relevant info and reported on it, so as to provide you with a "source"
Should they challenge what your source says? Or spend time finding every single reference to statistics they have ever seen and linking? Well, to be fair, your source has vast amounts of money and resources at their disposal with people who can sit and do nothing else other than put together "facts" which may or may not be correct and it is darn impossible for mere mortal MN posters to find the time to go through, fact check and then write out how the figures have been manipulated if they have been. The other poster presumably doesn't have the time to go back and find every single statistic and link them for you. But you could look for them yourself if you wish. Is what I think they meant.
I might be wrong, and they can correct me if so.
In the meantime, a word to the wise, a lot of people are very poor and suffering at the moment. A bit of respect would not go astray.