Landing on the heel isn't itself a problem. But it could be an indicator of a lack of momentum to get out over the front leg (among other things). It that's the case, then the fix is to work on increasing momentum. If that's not the case, then don't worry about landing on the heel.
As for the "reach" comment, I don't know what was meant by that. If it means reaching with the front foot/leg, then I can only guess that it is an attempt to lengthen the stride. But, IMHO, that's the wrong way to lengthen the stride because the weight stays back and there is no efficient back-to-front weight transfer and that impacts energy transfer up the chain.