I have now checked (and by checked I mean - calculated all United / Newton Heath wins from the beginning of time
I can confirm that United had 1.990 league wins before this season. This was indeed the 2000 win for United - I do however not now if it was the first club to do so - but I am gonna go with the guy who said it was. If he could keep track of 2000 wins - he should know that as well.
For the record
1907/1908 - win number 250
1927/1928 - win number 500
1949/1950 - win number 750
1961/1962 - win number 1000
1974/1975 - win number 1250
1987/1988 - win number 1500
1999/2000 - win number 1750