The Moon appearing at zenith indicates that it was directly overhead, or very close to it. This occurrence can happen depending on the time of night, your geographical location, and the lunar phase. Zenith occurs when an astronomical object is at its highest point in the sky, and this visibility is influenced by the Earth’s rotation on its axis and its orbit around the Sun. In your location in north-central South Carolina, it’s not uncommon for the Moon to reach zenith during its orbit, which is approximately 29.5 days.
The Moon’s position at zenith is also affected by its declination, which changes as it orbits Earth. In more detail, when the Moon’s declination is at or near its maximum north or south during this orbit, it tends to appear higher in the sky at certain points in the night for those at mid-latitudes like South Carolina. Each month, as the Moon moves through its cycle, there can be moments when it is optimally positioned to be viewed at the zenith in specific locations. Thus, your observation likely coincided with one of these optimal viewing periods. If you’re interested in knowing the precise times when the Moon will again reach this height, you could consult a lunar calendar or an astronomy app that provides real-time lunar positioning data.