I use the same pattern (plucking with thumb/middle finger at same time) for those songs to, but vary the rhythm depending on the "mood" of the song (please don't take this as an indication that I know what I'm doing). For some reason, I have not been able to master any kind of picks and even use my fingers to pick out the 3 fiddle tunes I managed to memorize. Can't pick out melody, but have learned a few runs which help.

The pattern you identified is one I used a lot. I learned it when I first started playing at 25 and it just stuck with me and I can't get rid of it.......