EOS Bandwidth in most cases refers to operations which writes to blockchain. So if you would like to perform any operation, which will cause that some new data will saved into blockchain, then you will need to have some bandwidth left, to perform such operation.
i mean - no. of simultaneous users fetching the EOS blockchain data.
Fetching data is another thing. All nodes will be part of p2p network. Node of such a network need to communicate with other nodes, to always have the latest block.
Someone who own a node (not necessarily a block producer node), can expose an API (Application Programming Interface). Very often such API will be exposed by block producers, just to provide useful service for community.
Usually such APIs provided by node owners can have some limitations, for example rate-limiting, password restriction, DDOS protection, etc. If a user/developer will find out, that there is no available API, which can handle amount of request which he would like to made, then always such a person will be able to very easily setup own node.
Very often developers use own local node to have very low latency. Such a node is synchronizing itself by p2p network with other nodes. You can have a local node, use its API, but you don't have to expose your API to anyone else, if you don't want to.