I think they did a perfectly good job and this is good writing and it's not indicative of their intelligence or maturity.
Haven't you ever got frustrated at something where you just are constantly cursing inside. That seems to be what spurred this on, simple as.
Unfortunately, I think you are right.
Recall that in Game of Thrones the young Arya (she/her) grabs a light fencing stabbing weapon with two hands and flails it about like a 12 year boy playing with a pretend broadsword.
Syrio, her teacher, proceeds to correct her and teaching the beginning fundamentals of swordplay.
The GP has used a simile cussing like a 12 year boy and could perhaps instead used braying like a donkey, bellowing like a sea lion, cursing like a sailor, etc.
The use of a simile does not imply that the subject of the simile is a 12 year old boy, a donkey, a sea lion, a sailor, etc.