By "throw a cup of water into the bottom of the oven", is he being literal? as in literally pour the water onto the oven floor? Is that safe? Or is it "throw in" in the colloquial sense of "put it in"
It is far from safe. People have accidentally gotten water on the glass window of the oven door and had it shatter on them.
Many people, myself included, use a Dutch oven like the Lodge combo cooker. The bread bakes in a small enclosed space and the water given off during the bake is sufficient to steam the space within. That and you get a very even heat from all directions.
Depending on the oven, the literal interpretation will reduce its lifetime, or may cause immediate failure.
Some failure modes of some ovens are quite dangerous. So, yes, it depends. Most modern gas ovens are safe, most electrical ovens are safe. Old gas ovens are usually dangerous in more ways than this.
When in doubt, you can always put a container with water there.
It’s best to buy a cheap cast pan, fill it with chain or bolts, and through it on that. If you want to get fancy you can get a metal colander and fill it with ice and put it above that.
Baking tray with lava rocks is a better option, but the simplest option is just to bake in a dutch oven with a lid on. There's enough moisture in the dough to create required amount of steam. 20 min with lid, 20 min without gets the job done very nicely.
