Neither has it been proven that it was the Syrian government. But the BBC and CNN have already jumped to their far-reaching conclusions. They might have forgotten the difference between correlation and causation. That the air-strikes coincided with the gas cloud doesn't necessarily mean that chemical weapons were used in the air-strikes. I'd say the Russian report has as much plausibility as ones by the BBC and CNN, which are not exactly unbiased sources when it comes to Syria, either.