STEM 
STEAM ;- )
for people, who admire artists and wish they were artists (I do), such as @bh
and like to learn new things.
Those oil paint have thick rough texture resembling actuall objects ie. grass. Created this way looks partialy like a semi-sculpture with 3rd dimension. Also long, overlapped strokes makes the feeling of grass stronger and adds some randomnes usuall for real-life objects. Also objects are overpainted over existing image according to its deepth.
I really see no similarity to the water color painting - John Singer Sargent, Siesta. For me they have nothing in common. With water colors you must plan in advance brighter area. You can overlap only with darker color to makes details or shades. And there is no texture other than on paper. Also soaking a paper with water paint makes soft shapes and images with lower overall resolution.
van Gogh grass, for me looks crisp and life-like, while "Siesta" is like foggy dream.
Yes, I can agree there is certain fogginess, I think, because the Mediterranean sun is too strong in the summer and blinds the viewer in a way, so nothing is sharp anymore. Maybe this is what so different styles/paintings nevertheless have in common, how the light works. If strong, but not too strong, the light itself makes things look more vivid, clear, life-like, 3d, as you say, on the other hand, if it is too strong, it blinds the viewer, I guess.
I'm just referring to this https://drawpaintacademy.com/grass-and-butterflies/?omhide=true
"The scene is depicted from a downward perspective, as if we are in van Gogh's shoes looking down at the marvelous garden and butterflies. This cuts the depth and gives the painting a relaxed, intimate feel. It's similar to Sargent's Siesta."
Arts perceiving is strictly subjective but such statement, for me, seems quite random only pretending to be the result of deep knowledge.