damon:

the tech apparently confused an overflowing refill tank with a "massive"
coolant leak. level still between min and max marks cold suggests either
not much overflow, say a cup or so, or refill tank was initially
overfilled.

coolant level should rise when engine is warmed up, as hot coolant flows
into the refill tank from the expansion tank, then fall back  to original
when coolant flows back into the expansion tank as engine cools. refill
tank is vented, and coolant can overflow through vent.

there is obviously no massive coolant leak.

dan