>> I doubt this is true. What makes you believe that?
> For example this article on Tom's Hardware Italy: [...] > It titles UDOO mix Raspberry pi and Arduino.
Whatever the article claims, UDOO may be similar in functionality to Raspberry Pi plus Arduino, but it's certainly not based on Raspberry Pi. As far as I can see (via Google translator), the article fails to mention in what way exactly UDOO should be based on Raspberry Pi.
> I thought at least they upgraded all the models to dual.
The pre-2 models all used the same single-core SoC.