Was HindII the first restriction endonuclease to be extracted?
The explanation here is quite simple: HindI, despite having been isolated/discovered before HindII, is a type I Restriction Enzyme, not a type II:


  A type I restriction enzyme from Haemophilus influenzae, Hind I, which requires adenosine 5'-triphosphate and 5-adenosyl methionine, was studied for its activity on transfecting and transforming deoxyribonucleic acid (DNA) [...] Most of the restriction enzymes from Haemophilus belong to type II restriction enzymes according to the classification system proposed by Boyer. These enzymes require only Mg2+ for their action in contrast to type I enzymes that require Mg2+, adenosine 5'-triphosphate (ATP), and S-adenosyl methionine (SAM). 


(Source: Biological Properties of a Haemophilus influenzae Restriction
Enzyme, Hind I)

Thus, in fact, HindII was the first type II Restriction Enzyme isolated/discovered, as it's well documented.



PS: As a bonus, here is a table with the main differences among RE types I, II, III and IV (Source: Thermo Fisher Scientific):

Type I:


Multi-subunit protein with both restriction and methylation activities
ATP requirement
Cleavage site a variable distance from recognition site


Type II:


Specific recognition sequence
Cleavage site within or close to recognition sequence
Generates 5′ phosphate and 3′ hydroxyl termini at cleavage site
Mg2+ requirement for most


Type III:


Two-part recognition sequence in inverse orientation
Cleavage site a specific distance away from one of the recognition sequences
ATP requirement


Type IV:


Cleavage of only methylated DNA
Cleavage site approximately 30 base pairs away from recognition site