Well the van itself wouldn't know if the oil is sythnetic, so the oil change odometer wouldn't reflect that. And they marked 3000 on your sticker so that they could make more money off of you. Theres no way yo tell by just looking at it... unlesss maybe taking a sample and raising it to a very high temperature to see when it sludges up (synthetics have a MUCH higher temp for this thatn dino oil).
Otherwise i wouldnt worry about it. Run it for the next 9953 miles and don't think about it.