Well yes and they do mention you shouldn't leak it but given that it's on your teeth, how much leaches? Given that it degrades over a year
The fluoride added to the drinking water in the US exposes you to many more times than using a fluoride tooth paste, so any leeching from this is likely inconsequential. There's also papers linked in the website and it appears that it's an improved version of the silver diamine fluoride treatment, which a quick search reveals is FDA approved.