The 1874 RLDS edition accidentally inserted an all before the phrase “those which fled out of the city of Moroni”. The typesetter for that edition was probably the one who made this error; most likely, he was influenced by the all in the immediately preceding phrase “all their fortifications”.
Summary: Maintain in Alma 51:24 the phrase “those which fled out of the city of Moroni”, which has no all modifying those (the reading of the earliest textual sources, including 𝓞).