Many Russian bloc aircraft use compressed air for operating various services, particularly engine starting, as it’s not affected by very low temperatures in the way that batteries are. This is fine SO LONG AS the air is kept dry by a desiccant system. If that hadn’t been maintained properly, any moisture in pipework / valves etc. would freeze. I don’t know if this particular aircraft uses air for the brakes, but it’s a possibility.
As an aside, pilots of smaller Yak & Sukhoi planes can often be seen walking around with their „jump starter“ – a small high pressure cylinder and hose…