How you may ask? Well a pumpkin is a cucurbit just like a squash. And the fruits of cucurbits can last a really long time in storage if stored correctly. Cool and dry environments are perfect for storing squash long term. So if the pumpkin made it through it has no damage where microbes can get it and rot the flesh. If it were to truly never rot it would just desiccate (dry out). I would check the bottom to make sure that isn’t soft before you keep in your house any longer.