I have seen these tables with those legs before, I believe they are made by a particular company.
The slump could also have been a lift, I have no idea if they had to heat the whole sheet and work quickly around it lifting, or pushing down, the edges. Or if they could work around it heating it more locally as they go.
If heating the whole thing and not using a flat former, I presume that can lead to the undulations.
Texturing a section is feasible, the pattern most probably comes from a roller. You can by panels with such textured centre sections.