The article says;-

"Engineers from Network Rail attended within 20 minutes of the accident and stopped all trains at that time."

Good job it wasn't a serious bridge strike - those 20 minutes of open line could have been 'problematical'.

Anyone know if this is standard procedure now? [to leave the line open after a bridge strike, until its examined] 

I thought it was standard practice to stop all services and check that the line is safe to operate.
Does that not happen?

I understand that each bridge has its own plan. For some this is advice from the signaller to proceed at 5mph. Whoever was at the scene should have advised Network Rail in any event.