Creating a nested array of objects from a sample schema

This worked great. I am running into a small issue though.

page["banner"] = generate 1
page["banner"]["category"] = set "category[2]", values: ["banner", "home"]

Expected

"category": [
   "banner",
   "home"
]

Actual

"category": {
    "values": [
        "banner",
        "home"
    ]
}

What am I doing wrong?