If this is true, it would rather resemble a historic miscalculation on the scale of Russia during WW1.
There are already ongoing comparison, e.g. @garvanwalshe and @KeohaneDan discussing on UK as the equivalent to Serbia. But from my perspective, that's not accurate.
Serbia had at this time a quite nationalistic drive, but wasn't divided as e.g. UK. It was a historic miscalculation to believe, that killing the heir of the Austrian monarchy would bring them closer to their pan-serbian dream but that's about it.
For one, their calculations where not too absurd. They were backed by Russia which would have been strong enough to defend against Austria. And the event as such kickstarted the war but wasn't the cause of it.
Brexit is not a proxy fight between several super powers, quite frankly: UK is not important enough and there are currently no conflicting partner having an interest to escalate things.
Russia on the other hand was, similar to Austria, quite motivated to make war. 1) Both Reichs were already crumbling, overstretched and overslept changes of modernity (in defense, administration and on social change).
While still being hopeful superpower, they already crossed their peak and were hoping that a war could help them to get rid of their domestic and geopolitical problems and find their way back to global importance. Sounds more like Brexit to me.
At the same time they forgot that their internal troubles restrict them in their ability to cope with an external threat of this magnitude. They underestimated the determination, strenght and ambitions of their counterparts too - believing the war is over soon.
Militarywise they were outclassed, looking at the economic capabilities of UK the situation is similar: hubris of key actors, nationalism among their supporters and utter ignorance of both towards abilities and interests of their opponents.
