Firsts and Lasts in Motorsports

[D28]

First WC event won by a non F1 legal car-Bill Vukovich driving a Kurtis Kraft/Offenhauser in the 1954 Indianapolis 500

OK I will bite and ask. Why is Johnnie Parson's 1950 Kurtis Kraft Offy not the answer here.
Would it have been eligible for F1 in 1950-51?