Well because it's obvious that the lair wasn't destroyed, that kind of gives light on the Pocket Dimensions theory. Possibly to enter it, he used warp speed when he hit the Tryno Lair, appeared in the Earths core and got into the pocket dimension. Him using hyper speed on impact could have caused the Tryno Lair to change position, if like at 1/10000th of a milisecond Lavos was maybe like 5km under the Earth, the moment he opened the pocket dimension, the Tryno Lair maybe switched place and went to that 5km under the earth whilst we still see like an illusion of Lavos crashing into the planet... Umm okay... Dunno if that will truely work but hey, anything is possible in the CT world.