yea I've read the interview about it too and I wouldnt say that there is any solid evidence that its true. Though I wouldnt say that its not out of the question.
Southern Mantis stance is more evenly distributed than compared to the WC pigeon stance, where lots of weight stays in the back. JKD def. does not suggest something like a WC stance since it inhibits movement (in certain ways). Honestly I dont think I have seen enough of the real JKD that Lee had, much of it is flashy demos and movies, which isnt the real thing. So honestly I can't say.
Also alot of JKD came from a big mix of many things. JKD benefits from all types of arts..or rather, all types of arts benefit from JKD.
But strictly talking about Southern Mantis, I would say the speed aspect of it. The strength and speed of Southern Mantis is heavily related, to have one you need the other. But back to topic. The main thing about Southern Mantis is to keep the arms extended, reducing the distance needed to travel inorder to hit someone. I mean if your hand was next to your chin compared to your hand being 1, 1.5 feet from your chin its obvious that the farther hand would reach the target faster. If you develop the strength then the hit will deal the same (or more) damage as well. This doesnt just apply to attacking but defending as well. You can block attacks well in advance if your arm is farther out by using the same principle mentioned above. This is the major weapons of Southern Mantis, the range of our arms allows people to function alot faster..and you know Lee was all about speed. Faster your fist, the more force it packs. Theres also alot of redirections and such when you're in trapping range and with the training can move the opponents arms and fists out the way pretty easily, opening him up for attacks. Its also very direct (just like WC). The main thing I find more "realistic" about Southern Mantis is the more relaxed stance. I cant imagine someone naturally standing in a pigeon stance but the mantis "Ma" (horse, not to be confused with horse stance) is very relaxed. Shoulder with apart, one foot slightly infront of the other, knees slightly bent, almost like your just standing there. Though I will say Lee prefered a more 45 degree stance, Mantis faces straight forward, but that all changes to a more 45/sideways stance in sparring (why? i dont really know). So I would say the speed and range of attacks and also the easily appliable stance is something that might have stuck in Lee's mind when he was developing his JKD.
"you're going to work till you wish you were dead and then keep going.."