What's the difference between...
"alternatively that the rogue aircraft wasn't a hang glider at all, but something resembling one – perhaps a paraglider"
Yeah, 'cos they look really similar - not ;)
Whilst I can understand the author not knowing this, if the Qantas pilots were close enough to file an airprox, they are highly unlikely to have mistaken one for the other.
These are paragliders:
This is a hang glider:
The suggestion they had to take sharp evasive action further confirms their identification, as paragliders are visible from much further away, due to their profile, whereas hang gliders can remain practically "invisible" due to theirs.