Why does a single assignment to one 2d array cell fill two cells at once in Javascript?

I have this code from this leetcode question:

function digArtifacts(n: number, artifacts: number[][], dig: number[][]): number {
    
    const land: boolean[][] = new Array(n).fill(new Array(n).fill(false))
    console.log(land)
    
    dig.forEach(spot => {
        console.log(spot, spot[0], spot[1])
        land[spot[0]][spot[1]] = true
        console.log(land)
    })
    
    console.log(land)
    return 0

};

With this input

n = 2
artifacts = [[0,0,0,0],[0,1,1,1]]
dig = [[0,0],[0,1]]

With this stdout:

[ [ false, false ], [ false, false ] ]

[ 0, 0 ] 0 0

[ [ true, false ], [ true, false ] ] **but expected => [ [ true, false ], [ false, false ] ]

[ 0, 1 ] 0 1

[ [ true, true ], [ true, true ] ] **but expected [ [ true, true ], [ false, false ] ]
[ [ true, true ], [ true, true ] ] **but expected [ [ true, true ], [ false, false ] ]

Why do land[1][0] === true and land[1][1] === true when they are never accessed?