Hmmm... I've not seen that before, mate.  It looks as though juice has leaked from the 510 into either the poly finish or the underlying wood and then discoloured from heat.  I don't believe it's charred wood.
Did this happen in one event or build up over time?
	
		
			
		
		
	
				
			Did this happen in one event or build up over time?
						
					
				
 