Well, the second article doesn't really imply that they are equal, but does directly state they most closely correlate as such, rather than the other way around. In general, Socionics treats it as such when comparing the two, though most prefer not to compare at all. Someone simply took some very heavy liberties on the Wikipedia article and it was popularized in the West, while being contradictory to the views of mainstream Socionics.
Socionics, and especially Model B, treat Leading as being the primary conscious element in regards to the external world, while MBTI, per Myers-Briggs own statements, does so only for the extrovert, and places Auxiliary in this role for the introvert, as spoken of in the second article.
This is an image I made for introverts Model B. I should point out, though, that there is differing terminology between the first and second article, with the first referencing the shadow, and the second referencing libido. I had to logic-through multiple scenarios to reach a model diagram that allow both to simultaneously exist. The shadow in article could be the same thing as the libido flow in my diagram or simply be his chosen terminology for vital Superblock in that article, or it could be the "flip side of the coin" that is our internal dual that sometimes manifests itself, or it could be just a reiteration of cross-block.
Model B rectifies lapses in Model A compared to Jung with logical consistency. All extroverted elements in Mental Superblock are Libido Transmitters, that exert energy to receive information, and Information Receivers. All introverted elements in Mental Superblock are Libido Receivers, that energy is imposed on to transmit information, and Information Transmitters. E.g., Se leads exert Force to receive Laws or Relations, either from themselves or others. Due to the nature of Mental versus Vital, it is implied that extroverted/introverted elements roles are reversed in Vital. E.g., Ne in Ego may be libido exerted for Relationships or Laws information, but in the Id, it would be Libido acceptance to supply information; that is, Mental is generally what we consciously "put out" to the world, and Vital is generally what we unconsciously take in from the world. (so basically a polar switch for E/I elements over conscious/unconscious line)