The overwhelming likelihood is that the moisture is condensation (we have yet to test a rainfly that had issues with the fabric or seam taping).
When a tent is pitched over wet ground, moisture from the ground/wet grass will turn to vapor which will rise and condense on the inside of the rainfly. Condensation is most likely to occur when the air temperature and dew point are very close together. Expelled breath from a sleeper/sleepers also adds to this moisture vapor and to the resulting condensation. Ventilation can help mitigate this.
Rain means that the air is saturated and can no longer hold any more moisture vapor: In a rainstorm, ventilation of a tent becomes even more important. Make sure to open the Baseline Vents of your Alto or Telos (lift up the bottom of the vestibule doors and attach them using the toggles) to create airflow up from ground level and out through the Apex vents.
One other factor is important: do not overtighten the tensioners at the tent corners/vestibules. Doing so may pull down on the Tension Ridge pole - the resultant inner tent shape may allow condensation to collect on the ceiling of the inner tent and potentially enter into your sleeping space.
Correctly pitched with the Baseline and Apex Vents deployed as designed, a Telos or Alto will mitigate condensation extremely effectively.