Hi Shaggy...
Neutrophils are a type of white blood cells. White blood cells fight infections and are, typically, elevated when inflammation is present. A lab result you had 8 years ago would have no bearing on what's going on now or even a month or year after it happened, because our blood make up is constantly changing - even from hour to hour.
That said, to answer your question...
1) Low neutrophils have nothing to do with hyperthyroidism... hyperthyroidism is more likely to cause inflammation in your body, which could cause elevated white blood cells as the body tries to fight inflammation.
2) The only reason a doctor should/would investigate Graves Disease is if you have symptoms of hyperthyroidism and/or lab results indicate increased thyroid hormone levels. If you did not have symptoms of Graves Disease (hyperthyroidism) at that time, the doctor did nothing wrong.