However, if you listen close to the r/t then the crew of 823j KNEW there was a TALL ship ANCHORED before they even started their engines...
So what! They may well have realised then that they hadn't got the numbers. Contacted dispatch for the relevant figures (which no doubt dispatch had to go searching for) and proceeded to taxy whilst awaiting the data. Unfortunately the data didn't come as quick as they had hoped, so when reaching the active they had to inform ATC they couldn't go. Perhaps dispatch were busy or couldn't find the data etc. etc., and the decision was made to shut down. I say again, YOU (nor I for that matter) haven't any idea what was going on in the F/D and between the crew and Dispatch.