You need to put these two styles

  div.col-md-6 > div.secText {
    /*Meant to mimic the spacing when in Tablet size for 1st 2 grid components*/
    width: 90%;
    margin-left: auto;
    margin-right:auto;
    margin-bottom: 16px;
  }
  
  div.col-md-12 > div.secText {
    /*Meant to be picked up in Tablet size for the 3rd, wrapped grid component and set
      different margin width so that it aligns with the unwrapped grid components*/
    width: 95%;
    margin-left: auto;
    margin-right:auto;
    margin-bottom: 16px;
  
  }

INSIDE of the @media (min-width: 768px) and (max-width: 921px) { block.

The reason it was happening is because you had col-md-12 class on the third block, and since those styles were outside of the @media selector, they were being applied in all scenarios.