Yes it is the norm at LHR. It was more in evidenced at the previous T3 arrivals, when they often actually parked at T1 or T2. To be honest I'm surprised they ran a bus for 5 passengers, usually if numbers are that small (and ET is more full) then the first bus is mixed, but still zooms off fairly sharply. I think someone does a numbers calculation, they are only going to run 2 buses unless it's a full 321 or 767, and if all of ET can squeeze into one bus then the first bus can be CE only. But for most bussed CE, and assuming no shortage of drivers - which can happen late at night - this has been the arrangement at T5 for the last 2 years or so.