Andrey
I think you have too much faith in an Army observer remembering the type numbers of the Luftwaffe. He could well have seen the 190 go down and know that it was a fighter alright but still report it as a 189 since he mixed the numbers, not the type as such.
Mind you he would not make any such mistake when it came to tanks, guns etc, his home territory, but aircraft may well have been his blank spot....
Now if the same Army guy reported both the 189 and 190 in his report, well that is entirely a different matter...
Just a thought
Cheers
Stig