I have an 06 and the wife has an 02.Neither one uses oil.We do have the ham can air cleaner with Screaming Eagle inside though.Might be the aftermarket filters that consume oil.I highly doubt aftermarket companies went through the same thought and engineering process that Harley did.If they did they would sell bikes not air filters and pipes.Oh and for the fuel injected guys,tuners.
As other members indicated - dry sump can get low & if it wasn't "empty" you're still good. Also, v-twins get dirty between changes - alot of metal slapping around in there. Previous owner could've been changing...who knows..?? Really miss my 05 - take good care of her & ride safe!
Every Sportster uses oil and its considered normal. I check my oil after every long ride and i eventually have to add a little but not very often. As somebody else mentioned this is a dry sump and they normally use some oil vs a wet sump system. Check it regularly and add as required.
New Sportys use oil for the first 5,000 miles or so. Your engine is absorbing oil as it's breaking in. It will be dark too until it breaks in. I had to add a 1/16 of a quart every ride until recently. I just did my 5,000 and now my oil is using no oil. Very normal.