You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information.
<?xml version="1.0"?>
<api>
  <query>
    <backlinks>
      <bl pageid="1" ns="0" title="Hackuarium" />
      <bl pageid="1729" ns="0" title="Main Page" />
      <bl pageid="1842" ns="0" title="Press kit" />
      <bl pageid="2130" ns="0" title="20160204 Board meeting" />
      <bl pageid="2396" ns="2" title="User:Bastien" />
      <bl pageid="2552" ns="0" title="20180329 Board Meeting" />
    </backlinks>
  </query>
</api>