People are not able to counter bristle back, he's usually winning the lane (in this case it was quite sad though, bristle wins vs am and bane). If he's turning his back to our team and runs, and everyone first concentrates on him, you could guess that something cannot work properly in that case. =D
And at the same time Prophet pushes another lane. But that's to be expected, anyway towers are far too weak imo. No hero should be able to kill a tower alone (no matter lvl and equip). Tower's damage/armor/hp should scale with time...^^