This Vortigaunt was presumably one of many Vortigaunts enslaved as a soldier/worker by Nihilanth, and was likely set free from this position when Gordon Freeman killed the Nihilanth. Like the rest of his kin, he either came to Earth through the disruption of the Resonance Cascade or the subsequent portal storms. By the time of the Combine occupation on Earth after the Seven Hour War, he and his fellow Vortigaunts have become allies to the Resistance and humanity.
