As I understand it, "long transfer" means the bag goes to the (central, robot operated) bag store instead of directly into the transfer system and to the baggage assembly into cans for the next flight. 2 hours is a bit too early for luggage to be assembled for the next flight so the bags go into the bag store - and out shortly after. It is essentially a direction to the people unpacking bags from the cans on the incoming flight to send the bag either to the bag store (long transfer), or to arrivals (not a transfer) or to be moved to another gate ASAP (short transfer). Next-gate-ASAP is for use when the bags for that flight are already being assembled, which is a bit less than 2 hours before.
... as I understand, those who know better are welcome to correct me.