So this is completely speculative I know nothing about this tragic case but yes it is possible for actions taken as a result of a psychotic episode to be both complex and planned. What makes it psychosis is that the person has become unlinked from reality and is experiencing delusions +/- hallucinations. However the delusions and the behaviour they drive may be very complex.
Eg if this was in fact caused by psychosis eg secondary to schizophrenia the perpetrators experience could be something along the lines of knowing with certainty that Taylor Swift is the antichrist, this being supported by experiences of her speaking with you telepathically but also sending cryptic messages by television / media / song lyrics, seeing her with your own eyes transform into the form of a demon etc, knowing with certainty that children are a particular dance club are not children but are actual demons in disguise because you can literally hear them whispering in your head and you can see their true form etc, plus you may be receiving direct instructions from God (eg only this course of action can save the world) etc.
Clearly I have just made that up (purely speculative and one of a thousand possibilities) but that's the kind of experience people with psychosis can have - they may also be unable to rationally question their psychotic experiences (eg to ask themselves the question "is this real?") because their brain isnt functioning properly to even give them a chance of recognising reality - I guess a parallel would be to being in a dream (or rather a nightmare) where no matter how crazy it gets you aren't capable of asking whether it is a dream.
People with psychosis are generally averse to violence as are normal people and actually psychosis leading to violence against others is v v rare (psychosis leading to self harm or suicide is far more common). So sadly I think it is much more likely that this is essentially misogynistic terrorism.
However, if it is psychosis the offender truly isn't responsible and I have a great pity for him. Psychosis is not a "get out of jail free card" because actually 1) you're pretty likely to end up indefinitely in a high security forensic mental health unit with no end to your "sentence", 2) severe schizophrenia and other psychotic illnesses have dreadful effects in themselves (emotional numbing, inability to function, loss of personality, frightening experiences including delusions, hallucinations) as do the (absolutely necessary) medications needed to treat them (medicines only really take away things like delusions and hallucinations and cant help as much with problems like feeling numb, slow thinking, apathy etc) - that's a life sentence in and of itself and you are also extremely likely to die prematurely, 3) if a reasonable measure of recovery and insight is possible (best case scenario) you are left with the appalling knowledge that you didn't actually kill demons but innocent children.
It's not easy/possible to fake psychosis and you wouldn't want to. You are better off just being a horrible terrorist criminal.