Vietnamese people always say : Xuân Hạ Thu Đông
Do 'mùa đông' (winter) and 'đông' (east) have an etymological link or is it just a coincidence?
They sound identical in Mandarin also (where they are "dōng"), and there it is just a coincidence.
just a homonym
I think that is an error.
In Hanoi we say mùa hè. Maybe in this particular expression (listing the four seasons) a certain order and word choice is mandatory?
This phrase is more like an idiom (referring to something lasting for a long time, i.e., 4 seasons). You can't just switch out "hạ" for "hè."
Tshun hā tshiu tang (in Taiwanese)
Xuân, Hạ, Thu, Đông