You need to establish some facts. Firstly, the car was sold in July but it seems the MoT runs from April. A 3-4 month discrepancy. What were the mileages at MoT and at date of sale? What is the mileage now? This is why we only do an MoT immediately prior to sale.
Secondly, an MoT is only a snapshot of the cars condition at the time of inspection. It is quite possible for the brakes to pass an MoT but become unroadworthy a week later. The MoT standard is actually quite weak on disc condition - I speak as someone who used to be an MoT inspector until 2018. Discs can be really quite worn and corroded and still pass, whereas a diligent mechanic would recommend replacement. HOWEVER we do not warrant friction parts (brakes/clutch) - BUT we do normally replace any friction parts that won't last at least 6 months or 6000 miles in our judgement.