Good thing Horner and Helmut are gone. 😛
Seriously, it might have been driver error or it might have been something with the car. Yes it was wet, but there was zero reason for Hadjar to be pushing hard. Ferrari was the only other team that went out in the wet so it was likely they sent Hadjar out just to collect some wet weather data.
Of course, this is the problem with this "private" shakedown. With the lack of official information, unofficial information is dominating the news feeds. But the teams and F1 only have themselves to blame for it.
The teams really twisted F1's arm for it because they want all the track time they can get with the cars before Melbourne, but they also demanded that the public and media be banned from seeing any of it. They remember the firestorm of 2014 when the new turbo-hybrid PUs were derided for sounding like vacuum cleaners and they also likely did not want the more technical-oriented sites dissecting their designs for everyone to see (and copy).
F1, on the other hand, wanted at least the media there because they didn't want the media idlily speculating about the new engine and aero formulas over the Winter Break. So they pushed back as much as they could, but it appears to have been mostly unsuccessful. So the teams were able to hire private and public security to try and lockdown the circuit and the surrounding square kilometers, while F1's official media was forced to drip-feed what little they could which opened them up to "massaging the message" to mask any problems (like Hadjar's shunt or Bortoleto stopping on track in the Audi).