when teenagers say they hate all religion, they only mean abrahamic faiths.

Yes a lot do this, though I would say a lot of totally cis and straight white guys often say this too from my experience, even very right-wing ones.
Most if they research the religious diversity of the world and many theological ideas tend to come to a less harsh stance on things, even if they're more anti-religious than not.
I think Alex O'Connor is kind of a good example of this.

Your statement isn't necessarily true, youre basing your statement off of, im sure, are very few personal experiences. First off, its not just all edgy teens saying they hate all religions, and its not just abrahamic religions theyre referring to either. For example, I am an atheist. I dont believe in any religion, or for that matter, believe any religion is correct, or morally right. That includes ALL religions, from christianity, catholicism, islam, to buddhism, satanism, taoism, and so on. Do I believe there are some teenagers who just say they hate religion because theyve never truly looked into it? Yes, absolutely. However, there is a good reason to hate religion, whether it be the beliefs, the morals surrounding it, or simply how somebody was raised. 

there is good and evil to be found among the adherents of any religion.

there are buddhist terrorists

there are hindu fascists

there are satanist neo-nazis

there are wiccan rapists

there are taoist murderers

you don't hear about it because you don't live in a culture where those groups make up majorities or have large amounts of institutional power. you live in a culture dominated by abrahamic faiths so those are the ones you hear criticized, because those are "the establishment" where we are.

the problem with religion is dogma. dogma is all poison meant to dull your mind and make you easy to manipulate, hence why large formalized religions are rife with abuse.

as an aside, when i went to find the local pagan/wiccan communities around me it was gross aggressive cult recruitment tactics and sex pest shit from minute one, every single place, every single time. even just meeting my then-S.O.'s "mentor" (who was literally thrice my age at the time) for coffee the whole ordeal was love-bombing, telling me that i'm a powerful indigo child or whatever this week's made up specialboi spirit identity horseshit is, and openly making gross and clumsy sexual passes - right in front of my S.O. i'll be steering well clear of wicca and paganism for the rest of forever, that was the single most toxic and abusive religious community i've ever seen in my fucken life.

NOT ABRAHAMIC. they just mean christiantiy and islam.

 JUdaism has NOTHING todo with the christian filth. the OT is a corrupted, delibarelty mistranslated and contextless version and EVEN WITH that level of mistranslation it still  contradicts the entire teachings of christianity.

For context they invented:

eternal punishment/hell 

obession with afterlife in general- Judaism is about bringing heaven into THIS world. doing mitzvos, charity and so on. NOBODY knows how the afterlife will exactly look like for sure, I know however there is temporary gehinom ('purgatory') for cleansing of the soul and reincarnation

uniersalism/proselytizing (its prohibited in judaism to urge someone to become a jew, unless they want to CHOOSE to convert themselves which takes one + year)

original sin

being "saved" etc

thinking BEING gay is a sin and gay peopel are going to hell

being transsexual is a sin

man-god 

human sacrifice, trinity