The main Joplin page under Searching says that the order seen after a search is "relevance". So it is a sorted list, but not by title or date.
Search results order has come up before and it also looks like a lot of work is currently being put into search and the order of results has been discussed (see GSoC Search Engine Project).
I must agree however that working on more than one note at a time in Joplin is currently rather awkward.