Just be a case of the fans have found their limit in terms of airflow and cooling.
Driving around you were no doubt getting aid from the actual speed of the car + fans, rather than the fans outright which in stop/start has lead to it picking up. If you had 5mins of moving (80km/h+) it would've come back down.
If you have heat shielding deflecting the heat, of course that will help - however I'd see it as almost inevitable that it will heat up to those types of temps. Ambient air temp also plays a factor, was it warmer than normal perhaps?
Also if there are larger fans/CFM, this might also help. Perhaps water spray for the I/C as well to get temps down.
Still as you said, 84 is still low and it's really not much of a drama.