[he_is_legend]

"Buys out" and "owns" apparently now mean the same as "rent for a small period of time" ...

[vineyardmike]

It’s common to say buying ad space. You have probably regularly heard an advertiser “buying a full page”. No one’s ever “bought” the whole thing, so the confusing language of saying “buy” in this context never came up before.

[shadowofneptune]

It's the physical bits of page space in reader's hands, in this case. The usage is pretty common for print ads.