No its just thermine for compound base od silicone. Silicone can be in lots of different variant.
We cant use ordinary silicone for sealing windows or doors, it must be silicone for heatsink. This silicone have good thermal conductivity.
Lots of manufacturers have their product secret, and they dont give that secret to public. But you can read manufacturer data and info linked with thermal conductivity of that thermal grease.
Yes. To be on the safe side, you can use dedicated electronics silicone rubber. But acid-free silicone compounds are also used for a number of non electrical applications.
??? All 1-component silicon rubbers are RTV (room temperature vulcanizing).
Heat sink paste is an unrelated topic. It's high thermal conductivity is provided by aluminium oxide powder or similar compounds, silicone grease or other fluids are used as filler.