The ILOAD output circuit is “powered” from the VDD rail (internal LDO), even though you might expect a high output current transient to drive a high current out of the ILOAD pin, the practical result is that the current-reconstructor circuit just runs out of compliance headroom and saturates somewhere less than VDD ( 1.85V, typ) . So – in other words, the ILOAD pin cannot be subjected to a self-generated overvoltage.
Furthermore – the 1.35V upper limit is the range for the accuracy is specified. The ILOAD pin is not limited to this value for safety; it just may not be accurate if asked to go above this level while reporting current. It’s not clamped at 1.35V.