The stockelementsfx.com site is being hit pretty hard today -- it was down / unreachable for me for a while -- so I only took a very quick look at what was available. While all the images appear to have been vector graphics initially, some are .svg vector graphics files, and many have been rasterized to the .png bitmap format -- the couple I downloaded were 346 x 500 pixels & 1000 x 665 pixels, both at 64 ppi with attributes = AI.
Most of the images you see on web pages are pixel-based, like photos, stored in files that record what every single pixel in the image should look like, its color and how light or dark it is. The larger the image the more pixels it contains the larger the file, and it gets more complicated because you also have bit depth or pixels per inch or dots per inch [for printing]. You'll usually see Vector graphics used for the illustrations in magazines, logos and type [type & the fonts you use are natively vector graphics]. Rather than individual pixels, a vector graphics file contains directions on how software should draw the image, e.g., draw a line from this point to that point, making the file much smaller and almost infinitely scalable -- the same vector image file can be used on a postage stamp or a billboard. Because vector graphics files are so much smaller than bitmap [pixel-based] files, and because they really are one size fits all, vector graphics have been extremely popular for clipart. While it is possible to create images that look like detailed artist's drawings, most of the vector graphics you'll see look like the much simpler clipart you're used to.
Creating / drawing vector graphics is very different than painting / drawing -- you create line end points, adjusting handles for those points to control the line's curvature. It tends to seem impossibly difficult for some, and easy peasy for others, so if you find the whole thing way too difficult you're not alone. That said, one advantage of working with a vector graphics file, e.g., the .svg files available in this package from Jasrati, is that unlike pixel-based images, you can open it in an app like the free Inkscape -- inkscape.org -- and edit the original image without Any quality loss. You can add or remove parts of the graphic, change colors, manipulate point handles to change shapes etc., which is easier than creating the graphic from scratch. Many image or photo editing apps can work with vector graphics to some extent, or you can use a vector graphics app like Inkscape to *Rasterize* the image, sort of taking a screen shot of what the graphic looks like to give you the pixel-based bitmap file a photo editing app works with natively [e.g., all the .png files that are also available].
wikipedia.org/wiki/Vector_graphics
adobe.com/creativecloud/illustration/discover/vector-art.html
coreldraw.com/en/learn/guide-to-vector-design/how-do-vector-graphics-work/