Does anybody know what this wet system is?

[Flintstone]

it’s upstairs on a job,

Not one I’ve seen before, these aren’t in the area they want tiling. wall has been took out in another area and exposed the system.

 

[Uheat - Jake]

Looks like a screed infill system where insulation is placed beneath the joists and then pipes placed onto that and then screeded level with the joists. But it seems they've skipped the insulation part and just laid it onto wood. Looks like they've already had a cut in the pipe or something from your first picture as it has a emmeti 16mm connector in the floor which is highly advised against.

 

[Flintstone]

Yes they had it repaired as it got damaged when the wall was removed. This system covers are large area upstairs, and into one bathroom that wants tiling.