I think you're reading far too much into that comment. It has a smiley. Try hearing it as though the speaker is smiling.
However, now that you raise the question of The Free Dictionary, there is a potential problem with the way they collate entries. They correctly cite each one. It's that citation which should appear here.
The Free Dictionary is in effect a directory of definitions, in much the same way as Google or Bing is a directory of websites. We wouldn't accept a Google search link and extracts from the results page1; each of those quotations would need to be explicitly referenced with the source. I believe the same applies to The Free Dictionary. And given that each extract is supplied with a citation all ready to copy and paste, there's not really any reason not to. You should probably add an "All via TFD" link at the bottom of a set of quotations, so they can be verified and other cross-references might be used; but the original authors of those definitions should be given appropriate credit when they are quoted here, in accordance with SE's referencing requirements.
While ideally a link to the original definition in AHD or ODO or wherever should be provided, it may not be necessary2 and it seems reasonable to me simply to add a usual abbreviation to each as cited in TFD. Your quote from TFD might look like
All from The Free Dictionary
That indicates the true source of each definition, and avoids the RTFM abbreviation, for not very much more effort.
1 This does make for problems when answers simply reproduce the content Google supplies from a
define query. Presumably Google have an agreement with their sources where they can omit any reference. I don't think we should endorse that, particularly when it's easy to provide cited references from original dictionary websites.
2 This is a pragmatic opinion on a practical implementation of the policy when applied to directory websites. Because it has a diamond at the bottom of it, this answer may change if the opinion is found to be wrong.