There is a minor inconsistency between Pokemon Showdown's Database and the game code for Pokemon SV.
In the code of SV the Vivillon-Icy-Snow pattern has an ID # of 0, meaning Icy-Snow is considered the default form.
However, on Showdown, just having "Vivillon" makes it default to the Meadow pattern. (Which I assume is because the Meadow Pattern was the first to be revealed.)
In this case, the default result for doing things such as "/dt Vivillon" or having it as just "Vivillon" in Teambuilder exports makes it come up as Meadow pattern.
To be consistent with the game code, and other databases, the default pattern that should show up for Vivillon should be changed to Icy-Snow, and Meadow should only come up when entering "Vivillon-Meadow"
BUG STATUS: NOT A BUG / WONT FIX This isn't worth fixing as it adds no value and impact's users teams.