Inconsistencies in the encoding of collections results in some JS arrays, and some JS objects?

[lukeify]

I'm converting the following PHP collections to JS variables:

    JavaScript::put([
        // <snip>
        'launchVideos'      => $missionObjects->where('subtype', MissionControlSubtype::LaunchVideo)->filter(function($item) {
                                    return $item->external_url != null;
                                }),
        'missionPatches'    => $missionObjects->where('subtype', MissionControlSubtype::MissionPatch),
        'pressKits'         => $missionObjects->where('subtype', MissionControlSubtype::PressKit),
        'cargoManifests'    => $missionObjects->where('subtype', MissionControlSubtype::CargoManifest),
        'pressConferences'  => $missionObjects->where('subtype', MissionControlSubtype::PressConference)->filter(function($item) {
                                    return $item->external_url != null;
                                }),
        'featuredImages'    => $missionObjects->where('subtype', MissionControlSubtype::Photo)
    ]);

Take particular note of featuredImages and missionPatches. They each have 1 member in the collection, once where'd.

Yet, the former is cast to a JS object, and the latter is cast to a JS array:

I am not doing any mutating on the front end, this is the raw output. Can anyone explain why this is occurring?