In most countries there's an element within the society that supports a xenophobic extremism.
In more simple English, there's always some idiots who want to spoil it for everyone else because for whatever reason, they can't bare to see outsiders infiltrating the community.
A lot of the time, the resentment is deep within, and never manifests itself, apart from perhaps "Lighthearted" jokes between friends (I'm trying to put this very nicely).
It seems that in this instance, the colonial population of Australia who comprise mainly of white folks from England and Ireland (historically), and form the country's majority are suffering some kind of tension, most probably caused by an insecurity that other countries are suffering in the name of terrorism.
This insecurity and perhaps other contributing factors such as economy (Foreigners are often seen as taking jobs and resources), has reached a point where an incident (That didn't have to necessarily be a racist attack), has caused a public opinion flashpoint, added to by people's control being lost from excessive alcohol consumption. When people are drunk, they will say what they think, and loose a certain amount of restraint.
Unfortunately, when things have got to this stage, there's not a lot that can be done. People have short memories and only time can really fix things.
There's no excuse for the attack on the lifeguard, but also there's no excuse for the rampage. It's one thing to have an opinion and demonstrate it, but another to do so in a violent and destructive way. Whoever was involved from both sides that caused social unrest should suffer the consequences laid down by the county's law.
On a side note, I'm absolutely astonished at the amount of people who consider the Lebanon as an arab country. In fact, a lot of people Ispeak to can't believe that there are significant Christian communities within arab countries. More often than not, opinions get distored and confused. I know of people who are anti-islam because of the terrorism, so are therefore targetted racially against people with arab complexions (Dark hair, olive skin,etc). Subsequently, they target people that are not Islamic, and also not arab, their distorted opinions based entirely on someone's appearance.