EPS concrete is basically concrete with EPS beads and a few other things in it like latex paint.
The fact is, polystyrene melts at about 200 degrees F. The flash point of DIETHYLENE GLYCOL (which is at least a component of many such cans contain, along with other components) is 255 degrees. So it seems likely that a Sterno flame can easily melt, if not burn the EPS in your bowl. This is surely not a good idea! If it melts, it will surely be giving off some fumes at that point too.
I won't bother to look at when latex paint burns, but do you want it exposed to a flame source?
I'd suggest this is a poor idea.
If you really want to make a matrix that will be lighter in weight than pure concrete, there are surely some better things you can add to a concrete mix that will lighten it, while still not being a fire risk. A quick internet search just found hollow glass beads for sale at a low price in various places. And skip the latex paint in the mix too.
I originally looked on ebay, under "hollow glass beads". What I found does look too expensive, usually hand made. Depending on how many you need, maybe buy some cheap costume jewelry necklaces, but you would need a few to make a big bowl. I would also check craft stores like Michaels, and I was told just the other day that there are stores that specialize in beaded crafts. So then I looked for hollow steel or aluminum balls. Wagner sells a package (25 count) of 1/2 inch steel balls, though I did not see a price.
Then I started thinking more out of the box (ok, out of the bowl.) As a woodturner, I could make a bowl completely out of foam (or balsa wood, which is also pretty cheap and light), by glueing up a block, then turning it into a bowl on a lathe. One could create this as a form, then covering the bowl form inside and out with a thin shell of pure concrete. That shell would absolutely be adequate insulation to prevent any problems. If you are not a wood turner, then I'd find a wood turning group. There are MANY of them around the country, probably one in any significant metropolitan area. Go to one of their meetings, then ask around for some help. I'd bet that at least a few people would happily turn a balsa wood bowl for you if you provided the wood. At worst, some pizza might work to grease the wheels.