I may NOT agree that it came from TikTok (as said on December 2020)
On May 5, 2020 "Wellerman" Sea Shanty by The Longest Johns posted on YouTube[0] (now has 6.5M views).
And only after that, few month later TikTok users starts to sing along to Wellerman.
FTR, On May 5, 2020 also few other Sea Shanties from The Longest Johns's «Between Wind and Water» (2018) album, uploaded on YouTube: "Santiana"[1], "Off to Sea"[2], "Spanish Ladies"[3], "Haul Away Joe"[4], "General Taylor"[5], "Mingulay Boat Song"[6], "Banks of Newfoundland"[7], "Sugar in the Hold"[8], "Wild Mountain Thyme"[9].
On May 5, 2020 "Wellerman" Sea Shanty by The Longest Johns posted on YouTube[0] (now has 6.5M views).
And only after that, few month later TikTok users starts to sing along to Wellerman.
FTR, On May 5, 2020 also few other Sea Shanties from The Longest Johns's «Between Wind and Water» (2018) album, uploaded on YouTube: "Santiana"[1], "Off to Sea"[2], "Spanish Ladies"[3], "Haul Away Joe"[4], "General Taylor"[5], "Mingulay Boat Song"[6], "Banks of Newfoundland"[7], "Sugar in the Hold"[8], "Wild Mountain Thyme"[9].
[0] https://www.youtube.com/watch?v=-KO7cofMJH0
[1] https://www.youtube.com/watch?v=nD4gLEBGSkE
[2] https://www.youtube.com/watch?v=r-OJtDapSuA
[3] https://www.youtube.com/watch?v=24O3dtse-94
[4] https://www.youtube.com/watch?v=2dIA6H9vLKU
[5] https://www.youtube.com/watch?v=3mVWlZqxM4k
[6] https://www.youtube.com/watch?v=B7OkqjVFmFA
[7] https://www.youtube.com/watch?v=E3qhmblFEL4
[8] https://www.youtube.com/watch?v=bVmmxbNm33Y
[9] https://www.youtube.com/watch?v=go6v6R5pD7A