It is not immediately clear whether uploaden and downloaden in German should be treated as monolithic words or as having separable prefixes. Therefore, geuploadet, upgeloadet, gedownloadet and downgeloadet can all be found in the wild, as can spelling variants with -ed. If you have only encountered one version per verb, that is by accident.
The general tendency nowadays for both is toward them being considered partially separable verbs: Separable for purposes of the past participle, inseparable otherwise (ich downloade, not ich loade down). Many people avoid them altogether.