Stadt (town) was derived from Statt - here's a good explanation of that: https://www.duden.de/sprachwissen/sprachratgeber/Stadt-Statt...
The name Hallstadt (not the two l letters) means Salt Town.
Or, actually "place". In a lot of location names of germanic origin "stadt" doesn't the current semantics, of being a town with > 10.000. More often than not it just means "place".
And "Hall" is an old term for salt. Many towns related to salt have it in their names, in many places of Germany and Austria. "Halle an der Saale" in Thüringen, Bad Reichenhall (Bayern), Hall im Tirol (Österreich), Schwäbisch-Hall (Baden-Württemberg) etc.
"Hall" is believed to be of celtic origin.
And the double l is important. German is a language where in the written form you look at the letters and you immediately see how it is spoken. A double vocal makes the speed slower, and a double consonant makes the speech faster. So "Halstadt" would be slow Hal (so more emphasize on the "a" instead), and "Hallstadt" would be a fast "Hall", similar in speed like the english "hell": little emphasize on the "a".
Lol, written vs spoken German is just as ambigious as any other language with too few letters in the alphabet. Just look at "ich" vs "ach" (and then of course there's dozens of local dialects that don't even have spelling rules and would need even bigger alphabets if "done right").
Source: Read it somewhere a long time ago, sorry.
Personally, I don't think the original misspelling merited any of this.
No indication that he is perusing medieval documents. Most likely Google/Gemini.