No, you are thinking of a criminal court, this is civil.
The idea of civil small claims court is to claim back one's consequential loss, on this instance they fine company claiming their £150.
The grey area comes in when they cannot prove a loss, and whilst there is a contract in place (which started when you parked there) they have not actually had a loss of £150. Indeed it is clear that the sum is disproportional to the parking violation, it is also very clearly immoral. Whilst they will get something, it will not be the £150.
It is very difficult for a private company to to fine and individual (see bank charges). Business to business is a little different when it comes to late invoices etc.