No, it absolutely does not mean you have cancer. Very few guys are the same size. Lots of guys have one hang lower than the other too. What you might have heard is that if one or both do not descend/ come down- the one that is stuck inside is very prone to having cancer. Or you might have heard that if one starts to get smaller if might have cancer. I am betting what you have is absolutely normal.
People may say offset testicles get thru better in tight squeezes, and it might be true, but men are built with a natural weakness by design; a bigger chance for varicose veins around the left testicle; the veins being prone to enlargement thru lifting or strain during bowel movements, etc. Some men, who check, will find an annoying wormy feeling mass over the left testicle, much worse on a hot day. Not to worry...it's treatable. This equals more body heat. The testicle is merely trying to avoid the heat by hanging lower. I would guess that the lower left testicle has evolved over time.