I mean it sounds like there's not good evidence that scalp massage works, but as for blood flow being important to hair growth: this is how minoxidil works. It is a vasodilator and increases blood flow to the scalp. So it's plausible that mechanically increasing blood flow could do the same thing.
Im not sure the accuracy of that video seen some of his videos years ago.
However I believe scalp size and blood flow/scalp tension are very relevant in most hairloss sufferers.
It gets lost in all the other, mainly nonsense, non anti-DHT stuff on here and other forums. At this point to me it's common sense that scalp size and scalp tension along with blood flow all play a part, and eventually over a long period miniaturise hair.
The whole thing is so complex and multifaceted that as soon as anyone mentions blood flow they get shot down.
It’s not completely understood how exactly minoxidil works to prolong anagen hair growth and increase hair diameter. There are multiple other vasodilator meds which don’t produce hair growth like minoxidil does. So increased bloodflow is probably not the answer.
Scalp massage won’t save your hair but it will make you money if you’re a YouTuber.