The only way to see the difference is by turning multisampling off in the Ultra setting and see if there's any difference between High and Ultra on screenshots and in vRAM usage.
This is what the article says and it has no relevance to the difference between Ultra and High settings. It only talks about antialiasing.
Ultra Quality
At Ultra Quality, everything looks better but in a more subtle than dramatic way. The most obvious improvement comes from the 4x MSAA setting which is enabled by default using Ultra Quality. Up until Ultra Quality, all antialiasing is handled by a post processing shader , which though powerful, can miss certain objects. For example, at High Quality, fences and thin lines form crawling patterns when you move passed them. At Ultra Quality, the addition of 4x MSAA removes most of the offensive moiré patterns.
This is what the article says and it has no relevance to the difference between Ultra and High settings. It only talks about antialiasing.