Does dress style mean attire, or is it specifically a style of dress worn by women?
For example: "What is the proper dress style for the interview?"
The confusion here arises from two meanings of the noun "dress".
1 : apparel, clothing 2 : an outer garment (as for a woman or girl) usually consisting of a one-piece bodice and skirt
In this particular use of the phrase "dress style", they are using the first definition -- a general purpose word for your choice of clothing.
"A dress" always refers to the women's item of clothing.
You are not being asked to wear a dress to the interview!