Yes, this is a very interesting feature, one that I have not previously observed through either real life chasing or photographs. That's why I remain hesitant to comment on this.
It looks to me like the storm was some sort of not-well-organized multicell cluster or the tail end of a squall line. The contextual picture shows a cloud formation that resembles that of a shallow shelf cloud. The scud at the ground is an indicator that air has condensed near the ground, likely in response to rain evaporation and the resultant cooling and moistening (i.e., "wet-bulbing"). This implies there was a cold pool advancing generally towards the photographer (perhaps spreading out left and right as well). This leads me to conclude that the vortex was the result of increased vertical vorticity being tilted and stretched by a buoyant plume coming in from the warm, moist region ahead of the cold pool. The leading edge of the cold pool acted as a lifting mechanism for the tilting, and perhaps there was enough instability of near-surface parcels to accelerate vertically enough, or fast enough cold pool relative flow to force parcels up and over the leading edge, to get just enough enhancement of pre-existing environmental horizontal vorticity to get weak tornado-like winds to develop at the surface.
If the above is the case, then this kind of fits into the landspout regime since it was a non-mesocyclonic circulation created by tilting of local vorticity, but not aided by mesocyclonic processes. However, landspouts usually occur in PBLs that are very well mixed (i.e., neutral lapse rate) and somewhat dry (allowing for deep mixing up to the LCL/LFC). I do not know the structure of the PBL in this case, but given the cloudiness, lapse rates may not have been neutral and there was probably more moisture (reaching now).
I've seen a case before when tornadoes formed at regular intervals along the leading edge of a cold pool in a highly unstable and highly sheared environment (and also extremely windy at the surface), and in association with a squall line not containing supercell structure. In this previous case, simple horizontal shear about the leading edge of the cold pool was a significant contributing factor in generating sufficient vertical vorticity to produce tornadoes with condensation funnels from cloud base to ground. These tornadoes were not related to mesocyclonic processes, and they were strong enough to cause damage to buildings.
That's about the most scientific explanation I can come up with for now.
