They might be referring to the 21M cap on bitcoins.

First, there's no intrinsic value. If a healthy company's share price drops to zero, I'll buy up as much as I can, making a profit on just its cash reserves. Bitcoin isn't "healthy" (or unhealthy); it doesn't hold assets; it is the asset.

Second, companies (hopefully) generate value and return it in buybacks or dividends.

It goes a little bit beyond your question, but Bitcoin on its own doesn't create value in the same way a company does. Investing in Bitcoin is much more like buying Turkish Lira.

If I understand bitcoin correctly (I probably don't); Mining a block is finding some numbers (maybe they all have to be prime?) whose product is a large number ending in a specified number of zeros. Hence the zero sum game comment :)