So what is sabr, then

Not the absence of tears. That has just been ruled out by the practice of the one who taught it.

Not pretending the loss is not a loss. The Qur'an names it as a loss.

Not silence in front of Allah, since a prophet took his grief to Him and said so in as many words.

What is left is narrower and harder. Holding on to what you know about your Lord while it hurts, and not letting the mouth say what the heart is not entitled to say. The eyes weep, the heart grieves, and we say nothing except what pleases our Lord. That is the standard, and it was said by somebody in tears at the time.