I mean, it's funny and ironic in that Alanis Morrisette kind of way. But it actually makes sense.
Fire hydrants are heavily engineered hunks of metal. Metal getting rammed into at speed is a great way to generate sparks. And lithium fires are scary as hell. There is areason ANYONE futzing around with lipos should have a bucket of sand handy and why, as the article states, first responders need to handle these specially.
It is a similar principle as to how you don't pour water on a grease fire.