Different net protocols are used for different types of download. A web page will use the http (or https) protocol, but a file download could use one of several different protocols, for example ftp or bittorrent. If you are with an ISP who uses traffic management, then they will probably not restrict http traffic, but they may throttle ftp or (more likely) bittorrent.
Plusnet have a pretty complete description of how they manage different kinds of traffic.