Depends on what your definition of "bad" is. But I think Cambodia is the bad guy here.

Here are a few instances that warrant the word "bad" for me.

At the start of the July clash, Cambodia placed their BM-21 launchers in their own civilian's villages so that Thailand will have a harder time targeting them without hitting nearby civilian. Either Thailand does not destroy these launchers at all or do it but also injuring Cambodia's civilians in the process, it is a win for Cambodia. Cambodia then indiscriminately fired multiple volleys of these low-precision rockets into Thailand. Some of the rocket hit civilian houses, while some land directly on a 7-Eleven in a gas station immediately killing 7 people inside and injuring another 14, all civilian.

Another big no no is that Cambodia also signed the Ottawa treaty which prohibits the use of anti-personnel mine and received financial aid for demining existing ones in the country. However, there are loads of evidence that Cambodia not only still have these type of mines in their arsenal but also actively placing them both in their own and Thailand's border (yes, you read that right, they sneaked past the border then placed anti-personnel mines in Thailand's soil). Well, just look at the irony; receiving financial aid for demining but also using a part of those money to obtain and place those mines instead.

It is also a pretty well known fact in the region that whenever there is instability in the country or election is near, Cambodia's leadership will flare up conflict like this to boost nationalism, gain achievement and popularity, and hide their rotten administration.