As the video points out, transplanted hair can thin over time. The key word being can. Generally speaking, the more aggressive your hair loss is, meaning the more you lost at an earlier age, the more likely this will be the case.
Most people do not go to Norwood 6 or 7 or bald this aggressively. So, I would generally tell most people not to worry about their transplanted hairs.
My humble recommendation would be, if you are Norwood 6 or 7 in your twenties, you should definitely be on a DHT inhibitor to preserve your transplant, otherwise you will have spent a lot of money and time for multiple surgeries and rolling the dice with your result.
In your 30s and 40s, well, you are probably safer. 50s even more so.