Does this hadith means it is allowed to pray in not mandatory prayers reciting al-fatihah only?

In sahih Muslim we find this hadith: > 'A'isha reported that the Messenger of Allah (ﷺ) observed two rak'ahs of the dawn prayer and he shortened them (to the extent) that I (out of surprise) said: Did he recite in them Surah Fatiha (only)? (Source sahih Muslim , sunan abu Dawood ) Can we conclude from it that our Prophet (pbuh) prayed this optional (nafl) prayer reciting only the fatihah in each rak'a? Could we conclude from this that this would apply for any other optional prayer too? Or does it just mean it is sunnah to pray it "fast"?