The said video is hiding or even confusing some important details. The text says, it uses "Edsyn FL22", which is a pure no-clean flux.
The colour of the applied paste looks more like solder paste, a no-clean flux paste won't be grey. I wonder, if it's a self elaborated
mixture?
With flux only, additional solder would be needed for a reliable solder joint. The solder amount present with a HAL (hot-air levelled
tin) PCB surface isn't sufficient. Only BGA devices can be soldered without additional solder.
P.S.: The Edsyn FL22 data sheet mentions usuage of an Edsyn "Mini-Flow" tip, a concave tip with a solder reservoir, similar to Ersa
"SolderWell". But in the video, a standard tip is used.