Since the drone shot is very gappy, I think the grass is swallowing a large number of species. He stated himself 25% loss which is beyond acceptable for commercial plantings and most contracts would require an in-fill. If he maintained it, would it have been higher? We can’t tell. He is obviously only shooting the best parts of the site too (which is fair enough).
Like you say, species and site selection may be helping, not to mention the consortium of weeds present may be less damaging than other sites. Not taking away from the effort but as we all know, planting the trees is 10% of the work usually.
Plus, I hate to say it, but just planting tall “trees” is not a forest. There are a number of other species missing from the planting. If the plan was to insert more species once the grass was suppressed then maybe it would hit “forest” status but being in an open paddock like that, natural recruitment is not going to be high. We have to remember that this is YouTube content, not high quality ecological restoration.