This study does not address a few major issues in regards to the conclusions noted, IE: nutrition, pre, during. post workout nutrition, and the trainee's bodytype and training experience. For example, if an ectomorph is going to do HIIT prior to weights, then go to failure on his exercises, and not fulfill his macro requirements by the end of the day, he/she will be burned out in more ways than one in a few weeks time. However, if a pure endomorph does 40 minutes LISS prior to training, eat at a level that favors his body type, he/she may see results. Endomorphs require a lot of physical activity. Even if only walking every day. This will be very advantageous.
As a general guideline, I can never see how doing HIIT before lifting is going to be beneficial, no matter what the goal... Fat loss and muscle retention, or lean mass gains. If you are depleting your glycogen stores with cardio prior to weight training, it's going to severely hamper recovery parameters. Both with CNS and mitochondria repair. I would separate both activities by at least 8 hours and results will come at a more optimal rate.