You are using an English word in a German sentence, while they are (almost correctly, downgeloadet) applying the rules for words lended from foreign languages. So unless you are doing it for some particular effect, their sentence sounds funny, but is grammatically correct, yours only shows, that you know how to correctly speak English.
Best examples of the same thing are the plurals of nouns ending in y: In a German sentence, the correct plural of Story (capital S) is actually Storys.
This looks wrong to most Germans, too. So now you basically have to guess, whether you can impress your reader more with your advanced and wrong-looking German grammar knowledge, or whether you should play it safe and not risk to look like your English is rusty.
Another great one are Deppenleerzeichen in English or English-German compounds, which basically no one gets right, even though the rule has no exceptions. Author of the article slipped one of those in, too.
I know because ich habe gegooglet.
Duden lists both "downgeloadet " and "gedownloadet" (note the final "t"). It observes that in printed press texts, "downgeloadet" occurs more frequently, whereas in online texts "gedownloadet" predominates.
I ran a full-text search of my entire Duden library for the word "downloaded" and it does not occur at all.
<duden>
downloaden: Das Verb downloaden »herunterladen« wird sowohl als trennbares Partikelverb wie auch als nicht trennbares Präfixverb verwendet. Insbesondere beim Partizip II finden sich beide Formen: Wir tragen stylische Jacken, haben Musik downgeloadet und den Ausflug gecancelt (Freie Presse). Hallo, mein Sohn hat ein Spiel illegal über Torrent gedownloadet (finanzfrage.net). In gedruckten Pressetexten kommt downgeloadet häufiger vor, in Onlinetexten hingegen gedownloadet. Beim Infinitiv mit zu wird in Pressetexten meist die Form downzuloaden verwendet. Die finite Verwendung (z. B. ich loade down / ich downloade) kommt fast gar nicht vor, hier wird auf das Verb herunterladen ausgewichen: Er lädt sich spezielle Software aus den USA herunter (c't). Amerikanismen und Anglizismen (1.3), Partikelverb (2.4).
</duden>
In French, even though "télécharger/téléchargé" is most common and "download" is not really used, I would definitely say "je l'ai downloadé" (and I would expect Quebecers to say mostly that). I have observed a tendency to avoid any conjugation ("je l'ai download") in younger tech workers but I don't know how representative my young colleagues are. It always sounds weird to me and sometimes leads to misunderstandings, in this case for example it's not obvious if the person is saying they "are downloading them" or they "have downloaded it".
In Dutch there is no other word than "download" and it gets conjugated like other Dutch words, "downloaden/downloadde/gedownload". And I always feel like saying "gedownloaded", I probably do it half of the time. I thought it was because my Dutch is far from good, but maybe it's just a natural thing if it happens for native German speakers as well.
I think the OP’s problem comes from “down” being used like a standard German prefix, which does sound really awkward. Foreign verbs in French are (almost?) always used like first-group regular verbs, the only alteration is the suffix. It feels less out of place.
I'd much prefer "downgeloaded" over this nonsense using "actual" German words incorrectly.
Vilken "den" gratisbakgrund (dvs som vadå?), vart lade du den, och ligger den kvar där?