I study FMA and I have no formal training in WC, however, when working empty handed, people sometimes ask me about my "Wing Chun" or they say "Have you done WC"? I think it is because the FMA and WC have many overlapping principles dealing with centerline, trapping, sensitivity, etc. I think this is why the two arts are taught side by side sometimes. Rather than 2 totally different arts like (TKD and Judo), they run mor parrallel with each other, which means facilitated learning in both.
Just my guess!