Is Absurdism really part of Existentialism?

i'm not
really informed in this topic, however i'll try to give an opinion, I guess you
could say it is part of existensialism... somehow in a really superfecial level,
cuz it's really subjetive

Absurdism
claims that, and I quote "due to one or more of these conflicts, existence
as a whole is absurd. It differs in this regard from the less global thesis
that some particular situations, persons, or phases in life are absurd."

“Existentialism
is a family of views and forms of philosophical inquiry that explore the
existence of the human individual and conclude that, despite the absurdity or
incomprehensibility of the universe, individuals must still embrace
responsibility for their actions and strive to lead authentic lives.”

where do I want to get with this? well, existentialism embraces this concept as well, cuz it wants to embrace the absurdisity of it all on a deeper level. However, I think it depends on each person's mentality or condition as a human, if I make myself clear idk

In my opinion absurdism is just edgy existentialism.

Existentialism is all abt make ur own meaning blah blah blah and absurdism is a branch of that that says "I'm existentialist but instead of rationally choosing my own meaning imma embrace chaos and go with the flow."

I consider absurdism to be the edgy younger cousin of existentialism, still valid, but also not entirely separate and unique as it claims to be.

This I think depends on your own subjective interpretation of existentialism is.

Some people see existentialism as a mode of thinking to find some kind of individual meaning, and use it as a life philosophy.

However some other people see it as a purely ontological interpretation of how we as people are born in with faculty and freedom to chose how we life our lives. (Sarte) 

To comment on your argument of the two ways of thinking being paradoxical, I think the reason why you end up with such a paradoxical take on it, is because you're seeing it as if they are the same thing, I think that absurdism is more a deviation from the principles of existentialism and compared to existentialism is more about how you live your life compared to existentialism and the more philosophically heavy truths it instead derives from everything around us.

Another interesting observation you could also see is sometimes people portray people who believe in absurdists as happy existentialists so I think you could also see it in that way.

So In conclusion I really think its how you define and see existentialism, as it is 100% a larger and denser philosophical idea then absurdism and absurdism in my opinion is more about how we live our lives. Sorry if this is quite confusing as I am cluttering my thoughts together quite a bit.