[teytra]

Probably just folk etymology (and from the 18th-19th century?).

Note that the county of Viken was established in 2020, (though roughfly based on a historical name).

The first documented viking raids to England was described as coming from Hordaland, on the west side of (southern) Norway, while Viken is/was on the east side (and partially in Sweden today).

Also, people from Viken was in old norse called víkverir, not vikings.

[dandy23]

I think you confuse what OP meant.

The words viking and Viken probably both stem from the word vik, as in bay. Any bay.

[teytra]

Or... Maybe both the word viking and vik as in Viken comes from the same verb vikja that means to move (away). The idea being that a vik is where the costline moves away from the "sea road", the "NorWay" ;)

By the way, another word used for Viken (when used for the Oslofjord) is Folden, which means "the fold", so it is where the costline moves or folds away. Also, the counties on the west and east side of Oslofjord was until resently Vestfold and Østfold (meaning west and east (of the) fold)