This seems to be explained in a FAQ from a previous year for this scholarship.
I do not have numerically weighted academic transcripts, can I still apply?
We require academic transcripts/official documentation showing specific subjects and how your overall grades were obtained. We require evidence of the progress of your studies in individual subjects, so that we can see, for example, whether your strongest subjects were in the areas in which you propose your specific research inquiry, or whether your grades improved over the course of your years of study. We require evidence of the subjects you completed and of their actual value, not just the one figure for their composite value. This information is required so that panel members can make appropriate and informed recommendations on the ‘academic achievement’ selection criteria. We would suggest you contact your University to obtain this information as your application would be deemed ineligible without this information.
So they want a transcript which has grades for every subject you took (and not just an overall rating, which is all that some very prestigious schools in England provide).
It sounds to me that what "numerically weighted academic transcript" actually means to them is one that has an overall GPA, as well as all the numbers that went into computing this value. Most schools provide this in their standard transcript; the most notable exceptions being the few U.K. schools noted above—I would guess that these schools are the ones that this criterion is directed towards.