Yes, it sure does look like a gunshot hole or two in the sides. If they ever used the tanks to burn anything you would want some side airflow to get into the tank.
When I am not burning in my open fire pit and just have a few limbs to burn, then I use a much smaller 55 gallon drum and I have about 15 bullet holes all around the drum at various heights starting near the bottom. You need good side airflow to help the fire stay lit and get a good burn.
The reason a gun is used to shoot holes in the drum is it is much quicker and easier to get holes in a drum or tank like that. I tried using a drill on my 55 gallon drum and the metal was way too thick to drill through. Those larger galvanized tanks are probably not as thick but still it is so much quicker to just blast some holes in them.