1. This is the full scan of your parcel:
China Post Register Air Mail Tracking System
Parcel No.RS236278940CN tracking result
2016-09-14 00:26:44.0 parcel center received
2016-09-14 02:53:23.0 parcel center customs scan
2016-09-14 02:54:38.0 leaving parcel center ，next station Shenzhen center
2016-09-14 03:14:58.0 Shenzhen Transit Station export security scan

2. As you can see the parcel was received by China Post here:
2016-09-14 00:26:44.0 parcel center received

3. Seller need to bring to China Post the parcel or have a company bring the parcel to China Post. When you get your tracking number it does not necessary means the parcel is at China Post physically. It means only that a tracking number was identify for your parcel and it's up to the seller to send or deliver the parcel to China Post so they can scan it and put it into the system.

4. China Post Security check and Customs check come after a parcel is deliver to China Post. I suspect the clerk register the parcel into the system and then after that it goes through the check. It's not the other way around because parcel could get lost that way.

5. As for the white lie the seller told you, you need to understand that all seller are pressure to give you a tracking number and send the parcel as fast as possible. Most of the time a tracking number is identify but the parcel is still in the hand of the seller because they got the tracking number electronically from China Post.

Hope this help.