I’ll bite. Most of the Vikings that settled England came from Denmark and Norway. Harald was usually well-travelled even for a Viking, having being exiled to Rus, and then later returning. The number of Vikings from Scandinavia who went to Rus, served in the near east, then returned to Scandinavia then invaded England (carrying their loot with them all the way) can’t have been many.

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.

> The number of Vikings from Scandinavia who went to Rus, served in the near east, then returned to Scandinavia then invaded England (carrying their loot with them all the way) can’t have been many.

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.