Stepped on brake when cruise control engaged and car accelerated. on 2005 Lexus GX470

When car was set on cruise control at 70 mph, I lightly stepped on the brake and the car suddenly accelerated as if I floored the gas pedal and went into passing gear. The difference was that it accelerated 5 times as fast when I stepped on the gas pedal. There is a slight delay when the gas pedal is floored causing the car to go into passing gear.
I will be taking the car to the dealer to check it out. Any feedback is appreciated.

Asked by for the 2005 Lexus GX470
press on the brake instead of the gas, genius!!