Is this a US based TA? Sounds like they may have translated AA's local language for "meal available for purchase" to "meal at cost". I don't think there is any way anyone on board would know the actual cost of a meal or that a meal would be offered that way. But as you say, you expect to be upgraded so it's a non-issue and worst case you're in MCE, so it's still free (depending upon what the FA feels is within the rules of MCE). Sounds like you have nothing to worry about.