So it will. But there is a huge difference between igniting and exploding - and anywhere short of (or over) the perfect ratio
The detonation range for a hydrogen/air mixtures (%vol) is 18% to 59% - pretty large (compared with gasoline which is in the narrow range of ~1.0 - 3.5%)
Igniting the hydrogen/air mix in the beaker would have resulted in an unconfined deflagration and therefore transition to detonation would have been extremely difficult.
In the case of AURA, this was confined, and even a slight overpressure during deflagration should have been noticeable.
In terms of burning as it slowly leaks - perhaps, but it's a helluva risky business hoping that the interior pressure of the actual reactor is low enough, and that the leak is slow enough, to allow that controlled, "slow" burn.
