I agree. Best forget which way the electrons actually flow and just assume current allways flows from positive to negative. It's only really necessary to understand electron flow if you are actually designing transistors or some other kind of semiconductor device. Not usually even needed to design circuits that use them.
Generally negative earth system means that the -ve terminal of the power source (battery or DC supply) is connected to the chassis or earth terminal.
Most system use negative earth these days. Can't remember last time I saw a positive earth system. Probably was in a 1970's car?
If you come across a positive earth system be very careful. Things like connecting up an oscilloscope or other test equipment to diagnose a problem need greater care to avoid accidentally shorting out the power supply. For example it's not allways safe to connect the oscilloscope earth probe clip to a voltage rail marked "0V".