What is the meaning of this hadith on the caliphate?

What is the meaning of this hadith - “The caliphate will be for thirty years, then there will be a kingship after that.” [Collected by at-Tirmidhi (2226) who graded it ḥasan, as did Ibn Ḥajar in Muwāfaqat al-Khabar al-Khabar (1/141); Aḥmad (21969) and deemed ḥasan by al-Arna’ūṭ; Abu Dāwūd (4646) who deemed it ṣāliḥ (acceptable); and authenticated by al-Albani in Ṣaḥīḥ at-Tirmidhi and Ṣaḥīḥ Abu Dāwūd] Source is Yaqeen institute - https://yaqeeninstitute.org/mohammad-elshinawy/the-prophecies-of-prophet-muhammad/#ftnt31 Was Mu'awiyas rule considered a kingship? Also, up to al-Hasan, it was a 29 year rule, not 30 - is 30 years just a rounded number ?