Unless you friend happens to live next door to you having the same ISP means little. There are many variables involved in the ping times but it is primarily a measure of distance. Internet connections also do not always go the most direct route.
You can see this by choosing other servers off the speed test site both in the city you live in and in other cities. You will see both the ping and download speeds can be different.
As mentioned run a tracert both on your and your friends connection and see where the difference it. It may not be possible to fix but until you know why they are different you will not know for sure.