I find this slightly misleading, though I do understand why no additional qualifiers have been added.
my experience - granted, its anecdotal, of being a player in 1 PF2 game (with a 1st time PF2 GM), and being the GM in 3 is while its true that beginner "players" can make "wrong" decisions that "will" lead to a TPK, its just as likely that new players and GMs, can make a "wrong" decision that will significantly "weaken the encounter" as well.
you forget to apply a condition. things get easier
you forget to apply a resistance or immunity.. same
you forget to synergize a foe's 3rd action by use of aid..
you outright forget to use their skills like demoralize, stealth, trip, grab, because they are not printed on the stat block "in your face"
you stand there and attack 3 times...
you cast the "wrong" spells that target the PC's high save
etc. etc. etc.
IME, its just as likely that new (and not-so-new) players and GMs can make mistakes that go both ways - makes encounters tougher by giving the opposing side openings, and easier, by not exploiting obvious combat tools available to you.. IME, things end up even.
inexperience is not only a one-way march towards player death
Cheers,
J.