I guess after Bitcoin reached its first ATH in 2017, some mainstream Media started referring to ALTs like XRP and ETH by the abbreviation of crypto. I started hearing crypto from that time, though I may be wrong this is my opinion.
Plus it is easy to write crypto than cryptocurrency and also it is easy to pronounce.
I have come to the conclusion that the term "crypto" came about because people wanted to use a more attractive name than "altcoins." The maxi in me will continue calling all "cryptos" altcoins! I will call coins I respect by their actual name, but as a group they're always altcoins.