I’d get a blood sample redrawn by the same lab you had it done from the first time.
Not sure how the blood drive people measure it, but if the method is different, your results may vary from the way they were analyzed.
Yes - it can drop that much or more - related to increased aerobic exercise (can decrease total cholesterol and increase HDL cholesteral, improving the HDL/LDL ratio) - better diet (lo-fat, high fiber, lo-GI, etc) and appropriate supplements (omega-3’s) - tho most OTC omega 3’s are at a pretty low attainable dose.
Just as likely is artifact related to (A) how fully fasted you were at time of blood draws; (b) composition of meal(s) prior to the blood draws; (c) use of medications; and (d) lab error.
I agree with getting a repeat done by the original one. Some of the tests used - especially for screening - are pretty imprecise.