This is an outdated teach, IMHO.
This will result in the front leg opening opening up early which will likely take the hips with it. It will also cause the lower-half weight to "stay back" which will minimize how much he actually gets out of the lower half.
This is a cookie cutter approach.
Maybe this coach views the hips rotating before the shoulders as a form of rushing? Regardless, it's the opposite of what should be done.
More cookie cutter. The front side is very important to timing and its positioning needs to "fit" each individual pitcher.
And overall effectiveness.