How did Old Turkic and Old Kirghiz inscriptions resemble each other?

The Old Turkic and Old Kirghiz inscriptions are considered linguistically similar. Both are associated with the earliest known records of the Old Turkic literary language, which include stone stelae found in the Orhon River valley of Mongolia and inscriptions discovered in the Yenisey River valley.1

These records are written in a script often referred to as "Turkish runes" or the Kök Turki alphabet, which was used by Turkic-speaking peoples in Central Asia between the 6th and 8th centuries CE. While the letter forms of this script bear a coincidental resemblance to the Germanic runic alphabet, the writing system is actually believed to be related to Persian scripts derived from the Aramaic alphabet, such as Pahlavik or Sogdian.234