first of all, you said he sent you a page? Was it one that had a link that said "click here" or somethign? certain coding will return the IP address or send it..similar to the way certain forums track our IP's.
Possible ways to slow down connection:
1) Ping/super ping. he may be using a program to "ping" you or rapidly ping you, slowing down some bandwith.
2) packet corruption. Sometimes when certain corrupt packets are sent, they have adverse effects on the connected computer. For more information on that, you'd have to check out other forums.
This is just and Overview
3) using file shares? it is possible, if someone was very bored and useless, they would transfer back and forth files from your computer just to slow down your bandwith.
4) also, there are other tools like port flooders and such that will effect bandwidth.

Any other specific questions? when posting be sure to include things like OS and computer type.