JD
It may have been non standard - but as long as it was safe - flexibility is a tool that is often to little used - and sometimes something 'non standard' like this is used because it makes the ATCOs job easier.
McDhu had every right to question it - it was unusual and it's always worth checking - but 'unsusual' does not mean 'wrong'. ATCOs seperate aircraft, they have a fair bit of latitude in the means they use to achieve seperation.
Think yourself lucky that QFE is not also used in the TMA!!!