You are talking about one operation that returns a different structure based on whether you specify the query parameter 'description' or not. That makes it difficult for clients to interpret the response, so that's not how you would want to design it.
I would suggest making two operations, and calling the second one https://localhost:8080/rest/getOrder (singular), to indicate that it returns only one object. The microflow for that operation returns a single object.
Can you share the REST/JSON standards that your integration partner is using? I feel pretty strongly that a single-item array makes more sense in the case where there is only one search result vs. just returning an object.
Do you use the same JSON structure in those 2 requests?
Because if it is defined as an array, then you will always retrieve an array.