That's ludicrous because first bikes are in their own lane and by your logic, the simple action of a car driver putting on their indicator precludes every cyclist from passing it, whilst each is in their own lane. You have an interesting POV that cannot work in the reality of everyday road use
(1) The 'bike lane' stops at the intersection. However, your 'own lane' theory is interesting because all bikes could then bunch up at the lights without illegally overtaking the front vehicle (already sitting there). Bikes that then took off/kept up with the front vehicle would then effectively have right of way over the front vehicle turning left because they had not overtaken to the left of the vehicle.
(2) I never said an indicator precludes every cyclist from passing it - quite the opposite. And if (to take my theory further) the front vehicle chose (or was forced - except by bikes illegally overtaking it) to merely sit at the front with its indicator on - I'd argue that it was no longer actually 'turning left' and bikes would therefore be free to pass on its left.