No, that's a bodge, (unusual for drain layers of that era as the job used to be an art), but they may have been limited to what was at hand (i.e. no bends), or it's a later adjustment to the original. I am in agreement with Ian, and recommend you replace with plastic.
I'd cut the last section of pipe you have exposed, (carefully), and then remove everything upstream of that, including the gulley. Chamfer both inside and outside edges of the cut pipe, (you dont want any sharp edges where solids can catch), and fit a Flexseal or similar coupling to the cut end to adapt from the salt glazed to 110mm plastic. From there, lay new plastic pipe, if there is no chamber nearby out of shot, I'd fit a mini chamber where the gulley joins. Carry on through to the stack, if it needs a slow bend immediately outside the chamber to get the right angle to meet the stack, thats fine. Suitable bend at base of the stack, and reconnect that.
Lastly, run to new gulley at appropriate position. Id look at using a 'Bottle gulley', and connect the rainwater pipe directly to the back inlet connection, then extend the waste pipe through to discharge under the grid. Whilst downstream may not be in brilliant and watertight condition, hopefully it is far enough away from the property not to cause a noticeable issue.