As you already seem to have guessed, it works via the provides mechanism - the texlive-amsmath
package has a provide for tex(amsmath.sty)
as you can see by asking rpm:
% rpm -q --provides texlive-amsmath tex(amsbsy.sty) = 2013 tex(amscd.sty) = 2013 tex(amsgen.sty) = 2013 tex(amsmath.sty) = 2013 tex(amsopn.sty) = 2013 tex(amstex.sty) = 2013 tex(amstext.sty) = 2013 tex(amsxtra.sty) = 2013 tex-amsmath = 2013 texlive-amsmath = 3:svn30645.2.14-4.fc20
There may not be an explicit Provide
tag in the spec file though, as the provides might be generated automatically by a script.