Tyre sizes help

[Steveblmk]

I looked up the specs of the baghira online before ordering a set tyres I ordered and have a 19/19/21 on front but the one on the back I saw online was 120/80/18 there a fookin different size tyre on my rear at mo then what was listed online . So wondering will the newly bought rear tyre still fir mine is a MZ Dakar baghire