Most people can not think or concentrate on 2 things at once
Of course they can. How about riding a bicycle and singing? How about sight-reading piano music? Or a choir sight-reading a new anthem? Or marching band members playing their instruments and reading their music while marching in formation?
Most people CAN think of or concentrate on two things at once. It takes practice, and training, but humans are capable of doing multiple things at once.
Just because I can’t spell rite or rmemeber html while posting on FR doesn’t mean other people can’t. I can, however, hold an image of Mary greeting Elizabeth while praying the Rosary, or Christ being crowned with thorns. Nothing difficult about it.
Which is the cross of Christ..biking or singing..?
The examples you gave are not MEDITATING on 2 things at once ..they are rote behavior..