A similar event happened a couple of years ago at the Jerez MotoE race track. In that case it wasn't any cheapo batteries or chargers but 18 hugely expensive electric racing bikes. Believed to have been caused by a short circuit. https://www.eurosport.co.uk/moto/motoe-reveals-cause-of-fire-that-destroyed-bikes_sto7206120/story.shtml
Then a few months later, another bike caught fire after the battery exploded when being charged at the Austrian race and again the following year yet another one caught fire at the Barcelona track while being charged.
If it can happen to top quality, well maintained racing motorbikes then it should be no surprise when a few cheap golf carts do the same thing.
Fires involving li-ion batteries are really dangerous as they burn so intensely