This person was asking about C++ though.
That’s a User Defined Struct (UUserDefinedStruct) which is different from a C++ defined USTRUCT (UScriptStruct). The same is also true for a User Defined Enum (UUserDefinedEnum) versus a C++ UENUM (UEnum).
The “User Defined” variants are assets and appear in the content section of the Content Browser, whereas the C++ versions don’t.
C++ defined UCLASS types (which are also different from Blueprints) do appear in the Content Browser under the C++ classes section.
I was the one who added the C++ classes to the Content Browser, but that was back in 2014 and I can no longer remember what the exact reasoning was. I think it was so that our BP and C++ samples appeared somewhat consistent if you were browsing them in the Content Browser.