Solidworks CAD application generates binary format STL which contains "solid" in top of file. Binary format STL’s header is 80 characters, and accepts any strings in there even containing "solid". But below method in defaultgeometryloader plugins checks "solid" in top of file, then calls to load Ascii format if true.
 

   bool StlGeometryLoader::doLoad(QIODevice *ioDev, const QString &subMesh)
    {
...
        if (!qstrncmp(signature, "solid", 5)) //<-- !!!
            return loadAscii(ioDev);
        else
            return loadBinary(ioDev);
 

  
It should not check "solid" if binary format.