but “viking” doesn’t appear on either page

it's why you can't understand history from reading wikipedia alone (not trying to slight you here)

the Vikingen poem, by Geijer, is what popularized the Vikings. written in 1811.
Sweden lost to Finland in 1809.
Denmark and Norway were bombed into bankrupcy by Britain, in 1807-13.

All of Scandinavia was getting simultaneously owned at a common point in time. There was a lot of anger, Geijer recognized this and wrote the poem, and it was memed into reality