-colour everything flat, decide where your light is, put bands of bright/dark colour depending on which bits are facing the light. Once you've got it looking roughtly like a 3d object, then you can think about hatching/dithering.
-i've switched out you black stripes with blue ones because (I think?) blue is a rough compliment for orange. You have to shade the stripes, as well.
-don't do so much outlining - it generally makes stuff less appealing.
-he still looks a bit off, because you've sometimes used straight lines where you should be using more organic curves. An obvious example is his spine, which is wicked straight. It should have a bit of a 's' shape.
Everyone: "cartoony" is a style. Pixel art is a medium. If he says he's doing this cartooney stuff for the first time, that's not an insult. This stuff, this picture in particular,
is cartooney. Don't go out of your way to be offended. Don't be dicks to people, especially when you first meet them.
pixel art is any art generated by pixels. so yes, just using the pencil tool on ms paint does make pixel art.
You're confusing pixel art with raster graphics. Digital photos, anything that comes out of photoshop, all of that stuff is raster graphics. If you zoom in on it, it's made up of pixels. Pixel art is raster graphics with specific restrictions, usually restrictions like those you'd have on an old computer, like "can't use more than 2^n colours" and "must be no bigger than X by Y, where both X and Y are freaking tiny numbers". There's a whole bunch of skillsets that developed under those restrictions, and understanding them will make you a better pixeller, but anything that fits counts. He's right, anyway. This is pixel art.