"running hot" seems like an ambiguous metaphor in this case. It could mean "they're doing very well", but could also mean "in imminent danger of failure", as in

"running hot" seems like an ambiguous metaphor in this case. It could mean "they're doing very well", but could also mean "in imminent danger of failure", as in a CPU or overworked engine. The latter might be what the parent meant. Or maybe they didn't, and their choice of words is unintentionally amusing and ironic.