As suggested in this Stackoverflow Link by @Alex Mamo,

To check if the data is from cache or from Firestore servers, you can use the following line of code:

String source = querySnapshot.getMetadata().isFromCache() ? "Local Cache" : "Firebase >Server";

Also have a look at this Stackoverflow Link by @Frank Van Puffelen, To detect if the results came from the local cache vs which came straight from the server by checking the metadata.

Also take a look at this Document and Link which might be helpful.