The term "Old English" is completely misleading in this context given how distant modern English is from that language. Both were spoken in England, that's about it. Applying the same logic to "France", should we then consider Gallo-Roman works like Ausonius's Mosella (c. 370 CE) to be "French" literature?

The Beowulf manuscript dates from around 975 CE and is written in what might be better termed Anglo-Saxon. How much can you understand from this random sentence: "þa me þæt gelærdon leode mine, þa selestan, snotere ceorlas"? ("So my vassals advised me well…) I personally can't understand a single word or even relate it in any way to the English I know.

On the other hand, the Sequence of Saint Eulalia was composed in "Old French" in 880 BCE and seems rather intelligible to me. I also just took a random sentence from the Chanson de Roland (c. 1100 BC) and can understand all of it: "Seignurs, vos en ireiz. Branches d’olive en voz mains portereiz, Si me direz a Carlemagne le rei Pur le soen Deu qu’il ait mercit de mei." I'd even go so far as to say that's closer to modern French than Shakespearean English despite being written in Anglo-Norman … Which also means it should probably count as being English literature if Beowulf qualifies…

I guess the lesson here is simply to remember that reality is always a lot more granular than we first expect and that any sweeping judgements on languages, countries, etc. over the span of millennia make very little sense. By that criteria, the linked article was pure clickbait to begin with.