Note that this is self-reported mindfulness. I don't find it farfetched that someone who's been taught mindfulness would self-report lower even though objectively they may have a higher degree of mindfulness.
This has been documented already. As you begin mindfulness practices you become aware of your thoughts. You then think “gosh, I didn’t have all these thoughts before” when really you did, you just weren’t aware of them.
I believe studies on this are discussed in Sam Harris’s book “Waking Up”.
I believe studies on this are discussed in Sam Harris’s book “Waking Up”.