Why is this function sometimes producing returns outside its supposed restrictions?

As an exercise I'm building a clone of the classic Nibbles/Snake game.

The game area consists of a two-dimensional array (rows and columns), and the player snake consists of another two-dimensional array containing coordinates for each cell in the game area that the snake is currently occupying.

I then have a function to create the apples that the snake is supposed to eat. This function returns a simple array containing an x- and a y-coordinate specifying the game area cell to put the apple. This cell should of course never be one of the cells that the player snake is occupying at the moment when the apple is created.

However, the function I've constructed sometimes creates an apple in a cell that the player snake IS currently occupying.

Can anyone spot the bug?

This is the relevant code:

const rows = 20;
const cols = 26;

const cells = createCells(rows, cols);
let player = [[1,1], [1,2], [1,3], [1,4]];
let apple = createApple(cells, player);

function createCells(rows, cols) {
    let cells = new Array(rows);
    for (let r = 0; r < cells.length; r++) {
        cells[r] = new Array(cols);
    }
    return cells;
}

function createApple(cells, player) {
    let positions = new Array();
    for (let r = 0; r < cells.length; r++) {
        for (let c = 0; c < cells[r].length; c++) {
            for (let p = 0; p < player.length; p++) {
                if (!(player[p][0] === r && player[p][1] === c)) {
                    positions.push([r, c]);
                }
            }
        }
    }
    let random = Math.floor(Math.random() * positions.length - 1);
    let apple = positions[random];
    return apple;
}