Those were parallel developments, but after Google standardized Unicode emoji for use with Gmail and Apple implemented emoji on iOS for Japanese market support,

Those were parallel developments, but after Google standardized Unicode emoji for use with Gmail and Apple implemented emoji on iOS for Japanese market support, Apple continued to expand emoji set with bunch of smileys and human upper torsos, thereby consuming those emoticons into emojis. I'm not well versed in those part of cultures, but IIUC, yellow smileys and semirealistic humans weren't focus of Japanese emoji implementations, whereas it is in Apple iOS emoji set.