There are two types of pagination in Portfolio page:
1. Normal Pagination
Its simple pagination, so everything will be loaded as the new “request”. Category filtering is applied only for current elements in that page.
2. Endless Scroll Pagination (Default)
This type of pagination uses AJAX so once the user clicks “Load More” it will automatically continue to load new items (if have) till the end of them. Category filtering is applied also for new items that are appended by clicking “Load More” button.
To change pagination settings go to Appearance > Theme Options > Portfolio > Pagination Settings. There you can set number of rows to appear and the pagination type, which is described above.