The tilemap is hardcoded into an array of sf::String. He doesn't really "load" the tilemap, he directly reads the array and draws it.
To draw the tilemap, he loops on every character in every string of his tilemap: loop from 0 to tilemap height (H) and loop from 0 to tilemap width (W). The character represents the type of the tile, P is ground, C is ?block, etc. He has only one sprite, and change its textureRect (with hardcoded values) according to the character read in TileMap[j], and its position too, then draw it.