The 4th photo is quite interesting, the one showing the steel column with the beams fixed to each side.
Left hand beam has a welded end plate which is bolted to the column and is also supported on a fairly heavy piece of angle which looks to be bolted to the column. This is how it should be done
Right hand beam is fixed to the column by ?????
Timbers look like 6x2 in that photo, which wouldn't be enough for the whole (5m ish?) span, but probably fine for half of it.
Looking at the first photo, there's a steel column which changes paint colour where another beam may have been attached to support the mezzanine.
I'd say there was a steel beam supporting the centre of the floor, with the timbers set into each side of it, and that steel dropped rather than the timber snapping. Sizes of timber and steel appear to be about right, but whoever did the job had no experience with structural steelwork and tacked it together with a small DIY welder.....