solr sort on an unrelated entity field

Question

My document structure is like this

<document>

<entity name="entity1" query="query1">
    <field column="column1" name="column1" />
    <!-- more columns specific to this entity -->
</entity>

<entity name="entity2" query="query2">
    <field column="column2" name="column2" />
    <!-- more columns specific to this entity -->
</entity>

</document>

In my query involving entity1 columns only, if I add entity2 columns in sort clause, why should the result be affected at all? My query is only on entity1 columns which are unrelated to entity2. Is it the case that solr apply the sort clause first on entire "documents" and then apply the query condition(s)?

Documentation reads -

If sortMissingLast="false" and sortMissingFirst="false" (the default), then default lucene sorting will be used which places docs without the field first in an ascending sort and last in a descending sort. Can someone please elaborate on the bolded text?

Answer 1

I think the last paragraph of my question had the answer in it. If field is missing, default sorting is used which is why my results look "affected".