Interesting what some image editing softwares can do to "claims" that are not supported by true and tested hard facts and evidences carried out on the water...
Planing in 4 knots wind is BS all the way, no matter what the sail size or board type is. A dedicated planing hull starts to plane at 7-8 knots hull speed, i.e., when the wetted surface is dramatically reduced to the last 40-50 cm of the hull that is in contact with water and when the hull climbs and pass over her own bow wave. Typically, there is a sudden speed surge from the 4-5 knots "schlogging state" to the 7-8 knots "planing state" when GPS speed diagrams are scrutinized by computer analysis softwares. BTW, a Formula can start and sustain the planing as of 6-7 knots of wind with no whitecaps in sight. This usually requires a 11-12 m2 jumbo sail and a lot of pumping skills.
The only explanation of "planing in 4 knots of wind" is in DTL conditions where the energy of the wave and not that of the wind actually pushes the hull to a full planing state. No big deal : surfer do that all the time in 0 wind...