One requirement to get an ATPL unfrozen is to have 1500 hours.
BA ask for only type rating and min 500 hours on type. So conceivably, you could be an Oxford Wunderkind with 250 training hours and 500 hours at FR and apply - you'd be miles away from getting your license unfrozen.
So clearly, BA mean ATPL (F) to mean a frozen license.
If BA had said they needed 2000 hours of which 500 were on type, then that would have been confusing, but wording it as they did, its clear they will accept guys with Frozen ATPL's.
OD :-)=