A GAD test is only a definitive diagnostic tool if it is positive. A positive GAD test means you are definitely type 1. A negative GAD test doesn't mean you definitely don't have type 1, about 25% of type 1 diabetics are not GAD positive.
It is standard and usual to make a diagnosis of the type of diabetes (1/2) based upon clinical presentation because there are limited tests available to give a definitive diagnosis. Antibody tests are only definitive if positive, they could be negative and you could still be type 1. Cpeptide tests only tell you if you are producing your own insulin, honeymooning type 1 diabetics will be producing insulin. Advanced type 2 diabetics will not be producing insulin.
GAD tests, I think, are only analysed by a limited number of labs, hence your long wait for the results.
Could you have waited 6 weeks for the gad results when you were first in hospital with blood sugar of 28 and high ketones? Or do you think you just needed insulin for that brief period whatever type of diabetic you were? The presence of ketones on diagnosis is a pretty reasonable push towards an assumption of type 1, especially if diabetes symptoms are reported to be sudden onset.
There are plenty of LADA or type 1.5 diabetics who do have a particularly strong honeymoon period where they are able to come off insulin for a little while.