Art style is different from copying artwork. Correct.
For example, both Pablo Picasso and Georges Braque were cubists. Cubism takes a subject and breaks up the subject into individual parts and then reassembles these parts. All Cubists have the same style - but Braque's "Portrait of a Woman" is not substantially similar to, say, Picasso's "Girl with a Mandolin" because the elements that make up the works are different. Only the style of the works is shared.
What your video drawings shared with the other video game drawings was the art style, certainly, but also the colors and the elements that made up the works - tree and tree placement, for example.
Whether a court on analysis beyond "ordinary observer" would find the works substantially similar is something I can't tell you. It's possible.
Your first concern is whether the original artist would find your work substantially similar to your work, enough so that a court is asked to determine if your work infringes on the other artist's work.
You should have an IP professional in your area do a comparison for you and offer an opinion.
Good luck.