No, "most" is a reasoned observation: Googling "how many people cheat", most research report numbers around 50% or above.

And =>51% is majority, hence "most".

(note I said "sooner or later", i.e. not in all of their relationships)

Honestly, cheating is like this huge elephant in the room: we hear about cheating all the time, yet we keep saying to ourselves that cheating is an anomaly. It's not, it's widespread. People are just in denial about this.

(BTW, I'm not saying this out of personal trauma: I've never been cheated on, AFAIK)