Here is my bestguess, but guess only.
Looks like someone topped it up with goat's milk. I hear that swiss goat's milk works best........but wait....only on leather.
More likely someone topped up with water, thinking that was the coolant reservoir.
Eiither way, unless you poured in some weird white stuff originally, Needs flushing immediately.
"No big deal", said the monkey, since it is not his car. LOL!
You will be fine, after he replaces your actuator and other stuff. Should only set you back $10-15k or so.
Fire your mechanic.