I don't know of any rule of English grammar that would lead to this interpretation. If you do, you should immediately write to the maintainers of these websites:

https://redis.com/nosql/key-value-databases/

https://www.mongodb.com/databases/key-value-database

https://aws.amazon.com/nosql/key-value/

https://etcd.io/docs/v3.4/learning/why/

https://riak.com/products/riak-kv/

https://rocksdb.org/

https://github.com/google/leveldb

http://www.memcached.org/

The Chicago manual of style tells us that one should hyphenate compound nouns where both nouns are of equal importance; common examples include "philosopher-king" and "nurse-practitioner".

Besides, the slash is arguably more often used to mean "or" (think "he/she") than "and".

Haha. Key-value is meant (IMO) to show the connection between the key and the value. You're right, it's not a "key value" store, where "key" is an adjective modifying "value" to show that is only stores the most important values. The "-", again IMO, shows that there is a mapping between each key and each value. But geez, I think we knew what was meant :-)

I love how somebody modded INFORMATION down.

And here we were just making fun of Reddit for this kind of infantile behavior.