It didn't. What you are referencing is most likely the adoption of the Julian calendar in place of the Byzantine one used in Russia as the main year count until the end of what was 17th century AD. Byzantines, much like Orthodox Jews today (traditional Jewish year count starts in 3761 BCE) counted the years from the creation of the world that was said to occur in the year 5508 BCE according to modern count. The idea was popular among Christians who wanted to create their own, unified and international calendar in place of multiple systems of year count that were based on various events, such as the founding of Rome (753 BCE) or ascension of Octavianus (30 BCE) in the Western Empire, ascension of Nabonassar (748 BCE) in Egypt or battle of Gaza (312 BCE) in Seleucid Empire, not to mention the intermittent counts based on the reign of subsequent Roman consuls or the Olympic Games.

The first proposals for such a count were noted from around 2nd century CE, with the Theophilus of Antioch being credited with the first recorded one, establishing it to what is now 5515 BCE. Later, other proposals appeared, although they remained the in the rangeof 5500 years BCE, as in the case of the date proposed by Iunius Sextus in early 3rd century (5503 BCE) or by Panodoros and Anonnios of Alexandria who brought forth the date of 5493 BCE. Finally, the Byzantine year count that replaced all previous ones has been established only in the Paschal Chronicle written by an unknown author(s) in the 630s, according to which the world has been created on 21st March (spring equinox) of 5507. Later, due to the different dates of the New Year, it has been shifted to 1st September 5508. The first known document bearing the Byzantine era dating are the notes from the Quinisext Council of 691 CE or 6199 BE. The Byzantine count has been largely used in the territories that adopted Christianity from the Eastern Roman Empire, including Kievan Rus and was retained in Russia.

Attempting to unify the year count as the part of the 'westernization' of Russia, Peter I issued a decree on 19th December 7208 BE (O.C.), according to which the Byzantine year count was to be abandoned in favour of the Julian calendar (where the year 7208 BE corresponded to 1700 AD). The misconception that there is a 8-year discrepancy between the Russia and the West most likely comes from the careless reading, as the Byzantine era ends with a number 8, while the corresponding year in Gregorian and Julian calendars is 0, but this misses the fact that the difference is not 8, but 5508 years.