The "insurgents" never claimed such a thing. They said the situation was not hopeless, they had reserves coming in, 1200 fighters who were trained on Russian territory. The report is simply false, based on a "mistranslation" of a speech. The "mistranslation" got around very quickly, as opposed to the correction, apparently.
In his speech, reportedly made on Friday at a peoples council and posted on a pro-rebel YouTube channel, Mr Zakharchenko said: The following reserves have been gathered: 150 armoured vehicles, of which about 30 are tanks and the rest are BMPs and BTRs [infantry fighting vehicles and armoured personnel carriers], 1,200 military personnel, who are there now, who underwent training for four months on the territory of the Russian Federation. They were brought into action at the most crucial moment.
http://is.gd/yMrpYk
The rebels, he said, had reserves of 150 combat vehicles, including tanks.
An earlier mistranslation of his words suggested Mr Zakharchenko had said the vehicles were on their way from Russia.
http://www.bbc.com/news/world-europe-28817347
The propaganda technique employed here is obvious and has been employed in Ukraine not for the first time now: Let's interpret incidents on the ground or what our opponents say in a way that seems to confirm what we want to believe and report this as fact. Others will pick up on these "reported facts", and eventually politicians will express their grave concern over such reports and at some point urging political action.