My thoughts exactly after numerous google searches.As with most heated metals, there is a potential issue of Metal Fume Fever...
https://en.wikipedia.org/wiki/Metal_fume_fever
You'd need to speak with experts to know at what temps silver might release any toxic fumes.
Its melting point is nearly 1000c so that won't be an issue, but it is a very soft metal, that could easily be damaged with items such as stir tools.
For sure, if used like the vapman, it might be possible for the user to melt things if torched for too long or release toxic gasses.Another question which would have influence on the answer to said question is what temperature the butane lighter heats the plate up to in a certain time frame - for e.g 30 seconds?