This is clear.
The data type of the variable, as such, is Number. This means that every time you read it, it may be a different numeric type. It can be Int32 now, and Byte next time, and Double some seconds later, etc.
You will also see "Number", I suppose, in UA Expert, if you:
1. Select the variable in the "Address Space" window (left center of UA Expert)
2. Inspect the "DataType" attribute in "Attributes" window (right top of UA Expert).
What you have shown in the picture is the actual type of the value of that variable at given point in time. It can never be a Number (because Number is an abstract type). But it happened to be Int32.
If you subscribe or read the actual value using QuickOPC, and then you look at what you receive (such as UAAttributeData.Value?.GetType()), you will also get Int32. And that is what you were looking at in UAExpert.
The DataType of the variable is available during browsing, and many/most servers will be able to provide it without having an operational connection to the underlying hardware/subsystem. So that's what suitable for client-side configuration.
The actual type of value at runtime, in this case (when DataType = Number) can differ from one moment to another, and the server won't be able to tell it to you without being actually connected to the underlying hardware/subsystem. Even UA Expert does not show it to you "by itself" - you actually need to drag the variable into the "Data Access View" - which is equivalent of Reading or Subscribing to the Value attribute in QuickOPC.
Best regards