I agree; usually these number are per serving.
Not to be snarky, but if you are trying to limit sodium, you should not be eating pop tart or frozen pizza. Processed foods are ALL high in sodium.
Do you cook for yourself at all? It's not hard to make nutritious, low-salt meals at home. Buy a whole chicken or chicken breasts, drizzle with olive oil and roast in the oven at 400 until juices run clear. Brown rice helps lower blood pressure and is SO CHEAP to buy.
Fresh or frozen vegetables are also easy to prepare. Our moms boiled the heck out of veggies back in the day, but I just roast everything...on a sheet pan, drizzled with olive oil and herbs (no salt.) I love basil, rosemary, oregano, cumin, turmeric, etc.
Look at the serving size. I'm guessing the pizza serving is one or two small slices,sometimes weight of the slice or serving is the determing factor that is the listed sodium mg. Serving size or weight is supposedly the amount of salt.