OM-B - DSC - 36 - 20 - ECAM Bleed page
"Low temperature is detected (only in flight), if:
- the bleed temperature drops below 150°C,
- the wing anti-ice is on,
- and the pressure regulating valve is in the open position."
So all 3 conditions must be satisfied for the amber indication to show up. If You did not have Wing A/I on, this leaves only two of those, and consequently, there will not be the amber indication.
The precooler is fed cooling air from a fan air inlet, governed by a butterfly valve. This valve is driven via some pulleys connected by a twisted wire rope with an eye at each end. I once saw such a picture inflight caused by one of the eyes broken out of the (quite flimsy looking) pulley arm. That caused the butterfly valve to default to fully open, an excessive amount of fan air rushing through the precooler and, consequently, a too low precooler outlet temperature.
MEL 36-11-04A applied and required disabling the onside bleed system as per any of the subpoints of MEL 36-11-01.