If this is a port of Sinatra that is an option to make a very small concise webservice. You can choose to do seperation, but if you want something very simple and compact a single file can be easier. We have a Sinatra app that has the model,view,controller, and tests in a single file that is less than 250 LOC. It would be more obfuscated to have 5 files of less than 50 LOC each (Some with as little as 4 lines).

If it doesn't provide any option for separation that is bad, but for micro services it can be really nice.