On culturing the young anther of a plant, a man got a few diploid plants along haploid plants. Which of the following might have given the diploid plants?

When culturing anthers, haploid plants come from pollen grains (generative or vegetative cells). Diploid plants result from contamination by diploid cells of the anther wall (2n), which are somatic cells that can grow alongside the intended haploid cultures. The exine is just the pollen outer wall and cannot produce plants.