Yes, Lambert did brand their own derailleurs. I have the same bike and I have most of the Lambert equipment on it. Also, I have had at least 3 others of the lesser model (white and red color scheme) and they had the same components including branded derailleurs.
There are stories on the web regarding the entire history of this bike including the infameous death fork. I have a couple of frames and forks hanging out at my favorite haunt Steve Willis' (The Bike Stand). I think Steve said he wanted to build up one so that leaves the other for sale/trade if anyone is interested. FF only, these are pretty light and thin tubing but are lugless versions. I believe I also have some miscellaneous Lambert parts that I will also sell/trade if there is any interest.