Two qualities accompanied joining the imam:
• Following (Mutaba'ah): following the imam's prayer.
• Being together (Ma'iyyah): performing the acts together with the imam.
For the Lahiq just described, following remains, but performing that missed part together no longer does. The person completes an equivalent of that accompanied performance.
The prayer itself is still performed within its time, so it is Ada. Its Qada resemblance concerns the lost togetherness, not the disappearance of the whole original prayer. This is Ada resembling Qada, also called non-pure Ada.
- Why the Lahiq’s Prayer Resembles Qada