Swedish surname: Andrain vs Andersson?

Question

I'm researching a Hilmer Andrain, son of John Andrain and Hilda Lund, whose family emigrated from Sweden to the US late in the 19th century.  Here they are in the 1900 US Census.  An enterprising FamilySearch genealogist has linked them to Anders Johan Andersson and Hilda Maria Lund in the Westmanlands Sweden in 1881.  It looks like a good match to my eye.  

Does this mean that Hilmer's LNAB should be Andersson?  Any thoughts on why the entire family changed their name to Andrain?  (They were living in Tacoma, where up through the 1970s at least Anderson was one of the top 3 surnames in the phone book.)

Answer 1

Well, at least the whole family went to America about 1883.

https://sok.riksarkivet.se/bildvisning/C0006154_00182 - lines 11-14

Eskilstuna, Kloster och Fors kyrkoarkiv, Husförhörslängder för Eskilstuna: Gamla staden, Nya staden, Carl-Gustafs stad ("Stadsförsamlingen") samt Gredby i Fors socken, SE/ULA/10226/A I b/29 (1879-1884), bildid: C0006154_00182, sida 1310

As to why they changed their name, it was so common for Swedish emigrants to do that, there's really no asking why in a particular case unless there is family lore.

Well, one explanation is that at this time there was a general trend in Sweden of adopting a surname, or freezing the patronymic last name of one generation into a fixed -sson surname.

Comments

So yes, Hilmer would be Andersson in Sweden - born before the name change to Andrain and at a time where it is reasonable to assume that children had the same last name as the father (rather than a patronymic).

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Thanks so much!  No, no family lore that I'm aware of anyway.  Hilmer was briefly married to a woman that my great uncle had been briefly married to, so I'm basically going down a rabbit hole here.