Custom Towing Mark Olfstead Illegal Towing of utility trailer Vancouver, Washington

My son borrowed my sm. utility trailer.  While in tow, the trailer came unhooked hitting a car.  Very little damage to the car or the trailer.  The police issued a ticket as in Oregon, the trailer did not need to be registered but in Washington it did.  A tow truck came to the sceen and told my son he was going to tow the trailer.  My son wanted to move the trailer to the side of the road so he could go buy a chain and resume his towing but the driver told him no.  Said he was hooking the trailer and towing it to the yard unless he could pay $200.00 on site.  My son didn't have that kind of cash so the driver hooked the trailer and took it.  I arrived at the tow yard 45 minutes later and had to pay $311.00 to have the trailer released at which time, the person at the tow business helped my son move the trailer (by hand) and they hooked it up and my son drove away, with the trailer. 

I understand the ticket but do not understand the tow.  The person in the tow office said we should have been able to move it to the side of the road and did not know why the driver hooked it up and took it.  I offered to give my credit card number to the driver so he would release the trailer but refused.  Told me to go to the tow yard to pick it up.

Was this an illegal tow?