What you have is the media setting the language up for the future. That way, when the authorities confiscate a regular Joe who's got 4 or 5 firearms, it'll be a "cache" or "horde".
The word "cache" is not used to refer to size or amount. Use of the word in the context of the new piece does not imply anyone thought the firearms found in Burress' home were an especially large quantity. From Merriam Webster's online dictionary:
1cache Pronunciation: \ˈkash\ Function:noun Etymology:French, from cacher to press, hide, from Vulgar Latin *coacticare to press together, from Latin coactare to compel, frequentative of cogere to compel — more at cogentDate:1797 1 a: a hiding place especially for concealing and preserving provisions or implements
b: a secure place of storage
2: something hidden or stored in a cache
3: a computer memory with very short access time used for storage of frequently or recently used instructions or data —called also cache memory