Lava flowing while disconnected from source

Superflat preset: 3;minecraft:bedrock,59*minecraft:stone,2*minecraft:dirt,minecraft:grass;1;village,biome_1(distance=32),mineshaft(chance=0.01),stronghold(chance=32 count=3 spread=3),decoration,lake,lava_lake,dungeon
Seed: -7993066103807340761
Coords: -1785, 62, 43
Lava is flowing onto the ground behind this blacksmith, despite not being connected to the source blocks. The hole in the rear wall was already present when I found it.