How did Mansa Musa contribute to the cultural diffusion of %region%?
Many Anglo-Saxons also served as Varangians as well! Particularly after the Norman conquest however.
My money, excuse the pun, is on trade. It’s not uncommon for coins from far flung realms to end up in coin hordes. For example Roman coins have been found in Celtic hordes than predate the Roman invasion of Britain by decades.
I really don't find this that unbelievable, especially when you consider that booty brought back from the Near East could be traded locally by Scandinavians. So it just takes one guy looting the Muslim world for the silver to make it to Scandinavia and then England.