Seems to me that it is, only I associated T1 with top.Not how that works.
In the picture there you are in the overworld T2 zone. There seems to be two parts going down to 2b. From the river and another place. You go down there. From T2b, you find the randomly generated dungeon temple at T2C. You are fighting this, and find the T3 barrier, the lava path down to T3. Earthquake. You die and respawn in the overworld, but the two entrances to T2B no longer exists there. You need to find that area again, with possibly new entrances and all progress towards T3 gone.
This will not be the case for permanent dungeons, but I am wondering about the randomly generated content they talked so much about.