The temperature was high enough to allow the formation of hadron/anti-hadron pairs, which kept matter and anti-matter in thermal equilibrium.
However, hadron-antihadron pairs were only abundant for a brief time between about 5×10-5 seconds, the time of the QCD phase transition, and about 7×10-5 seconds, when the temperature of the universe dropped below the pion mass.
At temperatures below the pion mass, most of the hadrons and anti-hadrons were eliminated in annihilation reactions, leaving the Universe dominated by photons, neutrinos and electron-positron pairs.
[2] Combining particle physics models with the standard Lambda-CDM model of cosmological expansion, suggests when expansion cooled the universe to a transition temperature around 150MeV hadron formation was favored.
From this time until neutrino decoupling, antimatter is an important constiutent of the universe.