The HOA needs some legal justification or authorization, typically found in the rules, for this: they cannot do anything not authorized by the rules or some other binding/controlling document (e.g. in condo communities, a master deed). Without some rule, etc. supporting them, they can't bar the fire pits. However, note that the justification does not have to be focused on propane table top fire pits--a provision giving them the discretion (or right) to ban anything they deem dangerous or which would increase their insurance premiums would likely support barring such fire pits.