files used on older feature phones, while "65" refers to the much newer version 65 of Opera for Android.
Several factors contributed to the success of the 65jar hit campaign:
Opera Mini JAR builds were particularly influential in emerging markets (Africa, South Asia, parts of Latin America) where many people used feature phones with limited connectivity. A widely downloaded build—what someone might call a “65jar hit”—could shape browsing habits in those regions for months or years.