Will the train seat withstand 120Kg? was I seeing things? Maybe the weight was more since the person had a backpack. But the load was extreme.
I calculated 5 mm deformation on the cushion. Could I have seen it? Well maybe. Stresses were far away from the plasticity limit, however the structure feels loaded.
From my analysis the structure could take even more load and wobble even more. Maybe the squeaking sound over exaggerated my notion of wobbling.
The light blue image is the deformed state, we can see the deformation direction, which moves in a expected direction.
In this close up we can see a slight displacement. But very small.
So my conclusions:
The heavy train traveller was safe, the seat could stand a few extra Kg’s of weight with some more camping equipment.
The design seems fairly robust, however it actually wobbles.