The temperature change can have triggered the root growth or the plant need more water to support it´s increased body mass. (A change of condition could trigger most things in orchid growth...)
I would check the media and the roots in the pot as massive root growth could be triggered by the need of more water, and that could be due to loss of roots . Just to be on the safe side.
Otherwise it is not unusual that a massive growth of leaves are followed by root growth.