That's end grain balsa core in the video and the holes were not routed out either. If the area of deck is that soggy the only answer is to rip off one skin. The usual problem is with foam cores and limited area around the holes drilled for fittings. Closed cell foam limits the moisture traveling unlike balsa which will turn to mush.
Drilling holes and injecting epoxy glue is a really good technique for bedding fasteners, but this video is not about that. I can understand why someone would give this a go first, before ripping off the whole deck. If done well, using an allen key on each hole and then drying each hole out with a vac bag and then injecting glue, it would give you some bond between both skins. This repair may have worked but then if the original problem was not solved, then the balsa would have still turned to mush.
Balsa can be a pain, especially on polyester boats. It is certainly a huge pain if it has to be replaced. A bloke near me had to replace about 1/4 of his topsides, deck and cabin because the water got in the balsa - months and months of work and huge money. So bed those fittings properly every time.
