America's oldest tombstone came from Belgium and belonged to an English knight

<Julius Ceasar> also specifically used the Latin word "Belgium" to refer to a politically dominant part of that region, which is now in northernmost France. In contrast, modern Belgium, together with neighbouring parts of the Netherlands and Germany, corresponds to the lands of the most northerly Belgae – the Morini, Menapii, Nervii, Germani Cisrhenani, and Aduatuci.

What else would you call the region, commonly known as Belgium during that time?

On Wikipedia, they would write that it "came from modern-day Belgium", which sounds like a time travel scenario to me.

You'll also see infoboxes overflowing with anachronistic place names, sometimes attempting to clarify the archaic ones. They're not supposed to be there.