Even more annoying is the equation of creationist = Christian. That occurs in the media all too frequently.
I would prefer "evolutionary creationist" to "theistic evolutionist" myself, but it is hard to dislodge entrenched terms.
I see it as part of the way words with general meanings become attached to particular meanings. This is a frequent occurrence in theological history.
"catholic" once referred to the universal church. Now it tends to mean "Roman Catholic". "orthodox" was once seen as a characteristic of the whole catholic church. Now it trends to mean "Eastern Orthodox" Similarly, "evangelical" was once seen as a characteristic of the whole church. Now, in Roman Catholic countries it means "Protestant". And in Protestant countries it refers to those denominations which rejected the Modernism of the early 20th century. One of the most egregious narrowing of terms is the use of "bible-believing" to refer to a small group of mostly fundamentalist churches, as if all Christian churches were not bible-believing. Likewise "creationist" no longer means simply "those who believe in creation", but "those who reject evolution--in whole or in part--as a process of creation used by the Creator".