From the article:
Russia has many miners, and this is partly due to cheap electricity. This is to the extent of miners mining cryptocurrencies in the residential blocks. In some cases, they break into power supplies to obtain free power and firefighters warn that this overheats circuits.
I suspect that this was the main reason that a fire broke out, you also see it sometimes when people steal power to grow weed for example.
It's not the cryptocurrency mining that caused the fire, it's most likely because this guy jerry-rigged something to get free power and did a very lousy job doing so.
...
Thought the same at first, but it's harder to steal electricity in apartment blocks and energy is quite cheap in Russia, so ne real need for that. If mining rigs were indeed the cause (it's not 100% confirmed), then it's most likely due to them overloading the circuit, i.e. multiple miners/other devices connected to one sockets via splitter.
Many of the old apartment buildings have electrical wiring hardly suitable even for the normal consumption, not to mention supporting mining hardware.
Remember kids - always ask a certified electrician for advice before converting your bedroom into mining farm.
Btw, here's the original article (with more pics):
http://siberiantimes.com/other/others/news/cryptocurrency-goes-up-in-smoke-fire-caused-by-bitcoin-mining/