"Prophet Muhamad was born year six hundred and thirty two"
Translation:Mtume Muhamad alizaliwa mwaka mia sita na thelathini na mbili
The lesson tips for the Numbers skill don't go into this, but your vague memory looks accurate, going by these examples at 2SeedsSwahili:
249: mia mbili arobaini na tisa
928: mia tisa ishirini na nane
1,364: elfu moja mia tatu sitini na nne
8,723: elfu nane mia saba ishirini na tatu
19,284: elfu kumi na tisa mia mbili themanini na nne
53,981: elfu hamsini na tatu, mia tisa themanini na moja
125,728: laki moja elfu ishirini na tano mia saba ishirini na nane
500,200: laki tano (na) mia mbili.
(As in English, you’ll often hear people add the “na” before the final consequential place: “Laki tano na mia mbili” rather than “laki tano mia mbili.” Both are correct.)
The extra "na" in the answer "mwaka mia sita na thelathini na mbili" above would fit the 2Seeds observation.
Could it be different in different versions of Swahili? (I think this course is supposed to be Tanzanian Swahili.)
It would be strange for them to get this particular word plain wrong, and it had both "mtume" and "nabii" when I looked up prophet here: