Or course, the person receiving the payment may not ship or send anything if payment is in review. It could be a preamble to limitation on one or both accounts. Hopefully not though.
Paypal actually does this randomly on newer seller accounts....it should say something in that email about how the sender of payment has nothing to do with the hold etc.....it should also tell them to ship the item still and that they are protected blah blah blah.....It is just a random thing paypal does.