The person remaining calm may still be using the conversation to avoid responsibility.

Calm is a manner, not a moral position. A level voice can be doing something quite different from what it appears to do: running out the clock, making the other person’s urgency look like the real problem, keeping the discussion in a register where nothing has to be decided. Whoever raises their voice may well be wrong, and whoever stays smooth may simply be better protected. Tone reports on composure, not on honesty.

Notice whether the calm conversation ever produced a commitment with a date attached. If it did not, ask plainly for one and let the answer rather than the manner tell you where things stand.