Mendoza, the hostage taker did not just see the police trying to enter the bus as well. Negotiations according to survivors were going pretty well, he did not intend to kill anybody (although he was obviously beyond the point of rationality of course) but after he saw the live news coverage of his brother, who had been brought to talk him out the situation, roughed up and arrested, he went crazy and started shooting people. Mr. Leung, one of the victims tried to disarm him but he was killed.
I agreed with what you have said... but I believe the most important thing in a hostage taking scenario, like the one in Manila, it should be tackled very fast. Before any hostage takers had the reason to act otherwise.
And the Philippines police or government or authority should really review their policy of media coverage. Sometime it is not good to give the media too much freedom. If that is not possible, then at least invest in some jamming device, so as to jam all electronic and digital signal that could be received in a precinity, and deny outside any electronic contact to the precinity, so the hostage taker would not know what is happening outside the bus.
Plus... it is stupid to rough out some hostage taker's relatives, friends, love one or even colleagues in front of him. Obviously that man is already irrational there really is no point of agitating him further.
From what I see the Philippines polices had lost all initiative that they should have otherwise exploited. And after that, they went about many other stupid things like continual allowing of live broadcast by the media, roughing out of hostage taker's relative (even cuffing him)... and did nothing or very little in terms of controlling the public... so much so that when bullets started flying, I think at least one member of the public was hit by the stray bullet.
Overall... the entire rescue mission is a big international SWAT community's joke.