I think that most of the time, with someone new to the hobby, when they get two frogs of the same species, they are going to have been raised together. They are going to purchase them from the same source. Why would they want to pay for shipping twice in order to get them from 2 different bloodlines? Especially if they are not interested in breeding. So generally, putting two frogs of the same species together will mean that they were raised together. But putting two frogs from different species together pretty much assures that you are grouping frogs that were NOT raised together. i.e. different pathogens and parasites.
Plus, and maybe this is old school, but I was always told that putting frogs together from different locations, could introduce frog A, to a pathogen or parasite from Location B. Frog A's population could have little or no natural defense against said pathogen.
I thought it was good advice that Michael gave him but in his next post the op completely ignored and discarded it.