isAfter and isBefore methods compare dates by millis (ignoring time zone).
In your example, the dates have equal millis.
System.out.println(londonDT.getMillis() == estDT.getMillis());
will print true.
Expressions
londonDT.isBefore(estDT)
londonDT.isAfter(estDT)
are equal to
londonDT.getMillis() < estDT.getMillis()
londonDT.getMillis() > estDT.getMillis()