I think it implies mechanistic playing on each beat of the bar (if you're lucky) and only on each beat in the bar of full 6 string chords with no light or shade and no use of internal variations of notes or variation of inversions. It's even more common in some styles other than folk.

For example while I'm no fan of modern Irish session tune playing, the guitarists often use interspersed double or treble time interventions leading in to the chord that is on the beat, and I wouldn't call that "strumming" at all.

One so often hears the question "Do you play the guitar or just strum"? It's rude and it's ignorant.