This form difference is not based on the game version, or weather, this Pokémon's form changes entirely on where it last battled. However this does bring in interesting factoids about it when the female version evolves. When a female Burmy evolves at LV. 20, it keeps the form it was in when it evolved

Grass Form The more commonly seen form of Burmy you will see is the Grass Form. This form appears when you battle Wild Pokémon or trainers in Grass, Forests or just General green areas. When it evolves into Wormadam, this form of Wormadam gains the Grass Type which adds to its weaknesses, it has a different moveset to the others and the following Base Stats: Types HP Attack Defense Sp. Att. Sp. Def. Speed 60 59 85 79 105 36
Ground Form The next Burmy form is the Yellow Ground Form. This form is obtained after battling in caves, ruins or on roads When it evolves into Wormadam, this form of Wormadam gains the Ground Type which adds to its weaknesses, it has a different moveset to the others and the following Base Stats: Types HP Attack Defense Sp. Att. Sp. Def. Speed 60 79 105 59 85 36
Steel Form The next Burmy form is the Pink Steel Form. This form is obtained after battling inside buildings When it evolves into Wormadam, this form of Wormadam gains the Steel Type which adds to its weaknesses, it has a different moveset to the others and the following Base Stats: Types HP Attack Defense Sp. Att. Sp. Def. Speed 60 69 95 69 95 36