How was 'Umar, may Allah be pleased with him, twirling his mustache and blowing into it, and does that contradict the Sunnah of trimming the mustache?

The Sunnah indicates that trimming the mustache is among the acts of fitra (natural disposition). There are commands to clip it short (ihfa') and to trim it (taqṣīr), with An-Nawawi and others preferring taqṣīr.

As for what was narrated about 'Umar (may Allah be pleased with him), that he used to twist his mustache and blow into it, scholars have responded to this by stating that 'Umar would let it grow long then trim it, or that this was specific to wartime to intimidate the enemy, or that what was narrated about him refers to leaving the two ends of the mustache, which are the sibālān.