I suppose it might be hard to understand without proper context. Most of these incidents happen in poor areas. Poor people with built up frustrations and little education sometimes don't make the best choices, Roma or Czech.
(some time before this incident, there was another one, where a group of wannabe nazis threw a molotov into a Roma family's window, which left a baby girl badly burnt)
Our second biggest (I think) minority are the Vietnamese and compared to the Roma, they managed to integrate much better. I think the major reason for this is their willingness to send their children to Czech schools and fewer lifestyle differences in their culture. They're seen as very hardworking and that's a big plus in the eyes of poor or blue-collar Czechs. Vietnamese kids speak perfect Czech and are well behaved (by our standards).
The Roma on the other hand tend to be loud, aggressive, confrontational and extremely tribalistic. The family or clan take care of their own and Czechs are seen as very much The Other, who exist to be exploited. Scams, theft, all kinds of lesser crime, plus social security money are easier to live off than work. (because, let's be fair, very few people would employ a gypsy. Officially, over 57% of adult Roma in CZR were unemployed in 2009. Unofficially I'm sure some of them do stuff like construction and seasonal work.)
Many Roma children rarely go to school, if they go at all, which further removes them from their Czech peers. They don't speak the language as well, they don't have almost any education and they can't get jobs (either due to lack of qualification, or because of discrimination), which pushes them into the "traditional" ways of making a living. Those who try and live differently are sometimes looked down upon and they're pushed out of the community.
It's a pretty shit cycle and it's been going for years and years. I often hear people say that during the socialist regime (pre 1990) there were fewer problems, because the state was hard on those who didn't want to work and who'd stand out, or wouldn't fit into the mainstream culture.
Somehow I doubt it was as rosy as described, but it sure as hell hasn't been getting any better.
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It varies though, some areas are better than others. I was born in one of the north eastern regions, regularly with the biggest unemployment rate in the country. And somehow, while there are still problems and ill feelings, the shared poverty sometimes pushes people together rather than apart. In my town many Roma and white Czechs live very similarly. My family was very much middle class, but I'd go to school with white kids who spoke and acted a lot like the Roma kids they lived next to, who in turn weren't nearly as bad as they're sometimes portrayed.
The English Wiki page on Czech Roma is a bit short, this auto-translated one gives more info:
https://translate.google.com/translate?sl=auto&tl=en&js=y&prev=_t&hl=en&ie=UTF-8&u=https%3A%2F%2Fcs.wikipedia.org%2Fwiki%2FRomsk%25C3%25A1_men%25C5%25A1ina_v_%25C4%258Cesku&edit-text=&act=url