The guy had a job to do, quickly determine who has it to make it and who doesn't and get rid of those who don't and bring in those who do. This is the same thing that basically every elite military unit does and in the same way, attempt to make them think they can't make it and give them no timeline on when the being hard on them will stop. They test will and mental toughness and not physical talent because success is determined much more by will and mental toughness than the others. That combination is the quickest way to weed out people who are not mentally tough, especially with ambiguity combined with being tough on them. One could view this all as him being a bad coach for being such an to them, or you can view him as a great coach for taking some of the most researched and effective methods for determining the intangible of will with a bunch of people he doesn't know and doesn't have the time to get to know well yet.
To me, he is quickly analyzing what he has, dumping what doesn't work and attracting the players that do. Doing this, putting people through all of that and seeing lots of people get weeded out is also another great method to form team unity for those who make it, taking care of peoples concerns of forming a team rather than mercenaries. All of them will immediately feel that bond and cohesion that making it through common hard experiences tends to bring to groups of people and you cant do that without making it hard or without cutting lots of people to make it special.