Like Bill said cutting or scraping in the wrong direction.
The second photo is an example of the back side of the endgrain.
It is the place I look to see how well I'm cutting, There is always a little bit or torn fiber on this part of the bowl.
Sometime you need a magnifier to see it.
The way I cut is foot to rim on the outside. While most of the cutting takes place toward the rim and a supporting fiber is behind each one causing a clean cut there is always a little cutting taking place parallel to the rim and on the back side of the endgrain there is nothing but air supporting the fiber so they bend over rather than cut.
It appear that most of your cut is parallel to the rim.
You could be using a scraper or pointing your gouge in the wrong direction.
Think of the wood as a bundle of broom straws with the straw running from the roots to the leaves.
The cleanest cuts cut a straw with one behind it.
On the outside cut foot to rim
On the inside cut rim to bottom.
Use sharp tools
Take light cuts at the end
Also walnut really shows the tearout as the growth rings are not joined to each other as strongly as most woods.
Have fun,Al