I have sent a SM on a couple of occassions, (been a quite a while though), after recruiting is completed to suggest to a new coach why it wasn't a good idea to challenge me in a battle, (IE higher prestige, more money, etc). But it was done as advise to help a newbie in the future. It is hard to judge the intention here. It could be friendly advice, frustration, a bluff, fear of running out of money, etc. I personally would probably send a simple reply: "I'm not sure what your intention was in sending this SM, but in all due respect, I'm not sure it is proper, and I feel very comfortable in my recruiting strategy. But thanks for the thought."