My boyfriend told me that when puppies lose their teeth, they eat them for calcium. Now before I doubt him and call him out, I want to be sure. So if anyone knows please let me know.

I don't think they eat them for calcium. But they normally end up swallowing them just because of the construction of their mouth, and their teeth are fairly small that it causes them no trouble. They can't really control it enough to not swallow them.
But I don't think they get useful calcium out of them...

I'm no expert so I may be wrong here :)

Puppies do swallow the teeth they lose. Many times I have noticed my puppy was chewing other than a chew toy and checked to find it was a tooth. Most of the teeth they lose, we never find, likely swallowed without being caught. Some of them even may go down with their dog chow.

Now as far as them eating the tooth for the calcium, that is speculative. They swallow everything else they get, why not the teeth? As for the body using the calcium? Likely the stomach acids quickly dissolve it. I never see any teeth coming out in the stools, although I clean most of them up, both at home and out in public. However the body is picky about its calcium. In fact, too much calcium can interfere with the body absorbing what it needs.

So yes, puppies do eat their teeth. Do they have have good reason? That is hard to say. I doubt your boyfriend is in a position to know.