Sadly, TileMaps currently don't have metadata support for individual tiles.
There's a pull request for that, but it needs some more work.
So right now, you'll have to manually check for the tile index where the collision happened. Something like this:
#Constants for your tile indices as they appear in the TileMap.
#First Tile is index 0
const TILE_FLOOR = 0
const TILE_WALL = 1
#Later, when the collision happened (tilemap is your TileMap Node,
#coll_pos is the position of the collision)
var tile = tilemap.get_cellv(tilemap.world_to_map(coll_pos))
if tile == TILE_FLOOR:
#Collision against floor tile
elif tile == TILE_WALL:
#Collision against wall tile