I would say no, in the main, they are bonded anyway with fixing screws, you are relying on the RCD tripping, unlikely with a TT earthing system, enough current can flow, to trip on over-current, it has to be TT as with loss of PEN, the door and door frame can become live in respect to true earth, so any metal outdoor shed or garage is treated the same as a caravan.
All it seems is built with self drilling screws and rivets, so if any part is earthed all is earthed. I have built a steel shed to house a sit on lawn mower, wanted a shed which was secure, so wood was a non-starter, we, the mid-week gang, as we are called, about 6 of us, all arrived with our battery drills, just as well, as by the end nearly every battery was discharged, likely looking at around 10 batteries between all the drills. Also, one impact wrench.
The electrics were done by another team.
My own garden shed is wood, so no problem with TN-C-S, however since I have solar panels, I do have an earth rod, so limited how much the DNO earth can vary from true earth. I was not worried about heating the building, so no need for insulated panels. As to how to take power inside the shed, don't want low down holes, where animals can enter, so outside socket, and penetration into the shed through back of outside socket.
Supply from its own type A double pole switching, curve B, bidirectional RCBO so I can if I so wish, fit plug in solar panels on the roof. I have a problem fitting an earth rod, my loop impedance tester has stopped working. So not worth buying a replacement, so if I wanted a TT supply cheaper to get a scheme member electrician to do it for me. Also since in Wales, it should be notified.
For the base of my shed, I used plastic pallets, so my shed is not connected to true ground, but the way the shed you show was screwed into the concrete, I would guess the earth loop impedance is likely around 100 Ω even without an earth rod, big question is if to use a copper coated earth rod or a steel earth rod, to avoid galvanic corrosion? I would make my mind up after taking the loop impedance readings.
