What do you call this design style?
I don't; that's graphic arts, NOT DESIGN. Screwing around drawing pretty pictures is NOT design. Design is engineering that incorporates art. What you have there is called a picture... and I'm not even certain there's enough there to even warrant it having an ART style of anything more than being "vector art"
Arun Raj
Product Designer @Hashnode
Icons of those style are called "filled-outline icons"