Here Oliver Cowdery accidentally replaced these with those as he copied from 𝓞 into 𝓟. Either reading is, of course, possible. The critical text will restore the original these. For a nearby example of this same error, but by the 1830 typesetter, see under Alma 24:10; there “these our many sins and murders” was replaced with “those our many sins and murders”. For a more general discussion of the tendency to mix up these and those, see under Alma 3:25.
Summary: Restore the perfectly acceptable “these Lamanites” in Alma 25:1, the reading of the original manuscript.