I don't know how long this has been going on but I just noticed it recently.
By default, impala-shell echoes the query after you type it, preserving the same capitalization the user entered. Except that the first word (i.e. the statement name) gets turned into all lowercase.
Notice how 'create' and 'select' were lowercased, while all other keywords were left with their original case. For me, the point of the Query: line is to have a conveniently copy-and-pasteable version of the original statement that I can put into a script or a document. If the case gets changed at all, that means some editing is required afterwards, which defeats the purpose.