Until 1991, the Internet was restricted to use only "...for research and education in the sciences and engineering..." and was used for email, telnet, FTP and USENET traffic—but only a tiny number of web pages. The World Wide Web protocols had only just been written and not until the end of 1993 would there be a graphical web browser for Mac or Windows computers. Even after there was some opening up of internet access, the situation was confused until 1995.
It shouldn't come as any surprise that, like other web host providers, A2 Hosting's unlimited plans aren't actually unlimited. It expect you to use its service like "similarly situated customers." This is like being on a highway. If everyone is going a few miles above the speed limit, you're probably okay, but if you're barreling down the fast lane past everyone else, you're probably going to be asked to slow down.