The TK A321 was completely in his right to stop before his parking position, if he/she deems it necessary for whatever reason. NOTHING illegal about this. Yes, obviously you inform ATC of this, but in a congested airport like IST, this can take some minutes, and is NOT a priority. That being said, in the Airline I fly for ( major B747 operator), we will not turn onto the gate if no marchaller or lead-in guidance. We do stop short if for example containers are blocking ( not always correctly visible perpendicular of the stand) or groundcrew/ debris in the area obviously.
HOWEVER... The PIC of the Asiana A330, or ANY Taxying aircraft has the legal obligation to stay free of all obstacles at all times, and “ But I was following the yellow taxiline” has absolutely nothing to do with that obligation. Have some Airmanship people! Taxi is a critical phase of flight that requires full attention of all flight crew members on the flightdeck. If necessary, deviate from the taxiline to keep clear of obstacles or better yet, stop.