As how was he to know if the taxying plane was not going to turn right for a back-track of the runway.
Notwithstanding the angle involved, did you see the speed it (the A340) was moving at? Handbrake turn maybe?! Only in the movies
That aside, I'm not disputing the fact that the decision to G/A was of course correct. Btw, just for info, I've seen quite a few late G/As at LHR, LGW and a host of other major airports. They are not that uncommon.