Aragorn's reluctancy, was it totally wrong?

[Kath]

"No!" said Aragorn, taking his hand and kissing his brow. "You have conquered. Few have gained such a victory. Be at peace! Minas Tirith shall not fall."

Might Aragorn not have just said this to placate Boromir though? So that he could die peacefully, not having to worry about having failed his people. Also, Aragorns words can be subject to interpretation. He does not specifically say "I will keep Minas Tirith from falling", simply that it will not fall. The immediate understanding of this would be that Aragorn intended to take over Boromir's role (in a way) but it is still ambiguous.