The video has this at 1hr:34min
Accordingly, the sea between Worthing and Brighton seafront possesses no curvature, or so little curvature, that within the parameter of the experiment, the curvature model is indistinguishable from the non-curvature model.
Conclusion to be valid
3) there must be no other factor that has not been taken into account that could be responsible for the resulting observation
What it is saying is that at the distance observed, 15km, the curvature and non curvature models both fit the results. Conclusion 3 says that everything must be taken into account for this resulting observation, but then IGNORES what I have already posted that the distance is so small compared to the circumference of the earth that it will appear to be flat. That does not mean the earth is flat.
Watching the whole video does not make it true, but it presents scientifically false information for confirming a false idea.