How long can a vehicle run if sugar was in the gas tank?

I purchased my used 2005 Sequoia 6 months ago. I have always driven standard smaller cars, so this was my first larger automatic V8 vehicle. I noticed immediately after purchasing my car that it would seem like my vehicle was stuttering when I would accelerate from a stop. I didn't think anything of it, just thought it was the type of engine. However, a week ago my car started to stutter really bad rendering it 'undriveable' and was making this loud cracking noise. I brought it to the dealership and I was first told that they tested my gas and I had apparently gotten bad gas (ie: water in my gas). So my ins adjuster went out and determined that it was covered and gave them the OK to proceed with repair. Well, today (a few days later) I get a call that they 'lowered' my fuel tank to clean it out and found sugar in the tank. My suspicions are high because my car is garage kept and you would have to access the inside of my car to open the gas door. Otherwise the gas door would have been obviously damaged. Is it possible that the sugar was in my tank when I purchased the vehicle 6 months ago?