Andy,
I have seen two versions of the "SIG trade deal" rumor on RCU and other forums.

1. SIG ordered a bunch of ARFs and did not have cash on hand to pay when they were ready. So, the ARF factory sold them to Nitroplanes.
2. SIG ordered a bunch of ARFs and rejected the shipment due to quality issues. So, the ARF factory sold them to Nitroplanes.

Either way, there were planes that look identical to the LT-40 and other SIG moidels on the nitroplanes site for a while and people who bought them indicated they received boxes with the SIG logo marked out.