The JSON you are seeing a JSON representation of the query and the data. It is the MongoDB Extended JSON (v2) representation of the BSON type.
JSON can only directly represent a subset of the types supported by BSON. To preserve type information, MongoDB adds this extension to the JSON format. That is what you are seeing in the logs.
For example, from the shell I created a document:
db.dates.find()
{ "_id" : 1, "dt" : ISODate("2020-09-23T12:10:15.710Z") }
When I query this same document, and the result from a MongoTemplate#find method:
List<Document> result = mongoOps.find(qry, Document.class, "dates")
result.forEach(doc -> System.out.println(doc.toJson()));
This prints: {"_id": 1.0, "dt": {"$date": 1600863015710}}
This shows the extended JSON representation of the MongoDB date field.