There's no excuse for celebrating beyond the hoardings. It's a caution every time and leaves players/ clubs risking serious incidents and punishments. The fact there was a gap in the hoardings, and no fans, is irrelevant. Hopefully there will be some internal discussions to remind players of their responsibilities.
The actions of the small minority of 'supporters' were disgraceful, but unfortunately would happen at every ground in similar circumstances. If there was racial abuse that is even more disgraceful and inexcusable but should be dealt with by police and club.