Question about reflexive verbs & adjectives and tense

Question

Mistaken (adj) = ошибочный

Can someone PLEASE explain how the endings in the following came about? They don't seem to be following the normal rules for adjectives and conjugation that I've studied.

I am mistaken = я ошибаюсь;
I was mistaken = я ошибался;
He is mistaken = он ошибается;
He was mistaken = он ошибся;
She is mistaken = она ошибается;
She was mistaken = она ошиблась;
You are mistaken = вы ошиблись;
You were mistaken = Вы ошиблись;
They are mistaken = они ошибаются;
They were mistaken = они ошиблись;

Answer 1

It's from verb ошибаться. Adjective ошибочный is used to describe something, not someone. For example

Он ошибается - He is mistaken

Ошибочное мнение - Mistaken opinion

But be aware that you can translate 'mistaken' as неправильно понятый (misunderstood).

Answer 2

Where the endings had come from?

Some blurring arise because you are blending two verbs (blending endings) that being structurally parallel in its aspect pair ошибаться и ошибиться.

Open in parallel ошибаться|ошибиться and take a look at its tables. 90% of native speakers are at all certain that the two verbs is blending into the one. So, at 90% you have a right ))

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and incidentally,

Я ушибла лоб.                       I have hurt my forehead. (I said: she)
Она ушиблась прямо о [...] .        She bumped straight into a [...].
Набила шишку на голове.             Get a bump on her head. (and paint the bump with iodine)
Оставив на ee голове хорошенькую шишку.       Giving her head a nasty bump.
Она сделала много ошибок.           She has made many errors.
Да, я ошиблась.                     Yes, I am mistaken. / I am wrong. (I said: she)
Да, я набила шишек в этой теме (ошиблась).  — an idiom
Нет, это ошибочное мнение.          No, It is a mistaken opinion. 

Idiom, usage with a context: набить шишек = have made errors