Not that I’m an expert on heresy or apostasy, but I think the questions is too vague, as to the circumstances.
I think apostasy has to involve some heresy ( I could very well be wrong on that). I guess we’re supposed to accept that these were willful actions and not under duress?
protestant (with “p” or “P”) implies a rejection of the Catholic Church authority, up or down the line, someplace. If they are REALLY protesting something, then it would seem to be simple heresy.
In my Catholic bible study recently, there was a formerly Catholic woman who left the church because she couldn’t accept the idea of confessing sins to a priest. The specific issue here might be a rejection of the sacred tradition of the Church which has established this rite. This would be analogous to leaving the Church because Baptism is administered not by immersion but by sprinkling or pouring water over the head.
In the US Church, it’s thought that many young Catholics simply drop out when they get into their 20’s – they don’t belong to anything.