Nowt dodgy
Educated guess would be that when 100 FS are credited to any player account, they randomly grab the next 100 server results in nano seconds and credit the total as a lump sum rather than per individual spin, not ideal but depends on how the FS are set up from the providers end, not the casinos.
Playing them out is as with normal play just the eye candy as has been discussed numerous times and seems something most of the community agree on (minus the 'rigged' brigade of course
)
I could of course be totally wrong!