the answer is already there. as you just have to read what you just posted
But do say they "manage traffic" at peak times. (what do they do to "manage traffic ?)
that means: they see what you do, and they cut down your speed. easy as that. Most of the ISP does that allot, and usually excuses it with that they need the speed to the other user so they can surf the web with fast speed. and dont some user taking up bandwidth