They are not grammatical errors since the sentence structure is correct once you replace the erroneous word with the one the author obviously intended.
So I would categorise those mistakes as spelling mistakes influenced by homophone confusion.
english.stackexchange.com/users/2614/RedGrittyBrick
I’m not sure whether there is a special name for this kind of spelling mistake, but I’d definitely call it a spelling or typing mistake.
The writer would no doubt have pronounced it right in speech.
In fact, I suspect that the most common spelling mistakes are those in which a writer subconsciously confuses two similar-sounding words or parts of words, even though he probably knows better, as in * negligable , * interchangible , * percieve ,
*retreive,
* their crazy , * they’re house , *
it
’s body , *
its mine , etc.
english.stackexchange.com/users/3036/Cerberus_Reinstate_Monica
There's no special name for it beyond: typo.
'quiet' and 'quite' mean two very different things; one is an adverb meaning 'very', the other is an adjective mening 'silent'.
their pronunciations are different enough; in GenAmE, they are not homophones (I don't know about other varieties).
Transpositino of two characters, especially at teh end of a word, is a very common typing error.
surely the writers didn't intend the words as written, so they are neither grammatical error or spelling errors.
english.stackexchange.com/users/4972/Mitch
Quiet/Quite might be considered a homophone depending on your accent.
Other common homophone (heterograph, specifically) mistakes are: Their/They're/
There Your/You're to/too/two
english.stackexchange.com/users/3433/Stephen Furlani
Since it's the person's intention to use it in a certain context, it is a misspelling.
If they were convinced that that was the way it was spelled, however, and spelled it that way, it would be a lexical error.
english.stackexchange.com/users/363829/Marcus Hendriksen
Semantic error.
Meaning is not logical.
english.stackexchange.com/users/24666/Chris
Look at this sentence:   It wasn't  quiet  what I wanted   And this one:   The music was too  quite  for me   Obviously  quiet  and  quite  are mixed up. Is this considered a spelling mistake? In both cases the words are valid, but used in the wrong place.   Is there a special name for these mistakes? Or are they simply grammatical errors?
Mixing up "quiet" and "quite": spelling or grammar error?
english.stackexchange.com
<grammar><orthography><terminology><errors>
english.stackexchange.com/questions/9396
english.stackexchange.com/users/3864/user3864
These are not grammatical errors since the sentence structure is correct once you replace the erroneous word with the correct one. As a result, these are probably spelling mistakes influenced by homophone confusion. Aside from the word "typo", there is probably no special word for this. Some people would also call this a semantic error since the meaning is not logical. This could be seen as a spelling mistake and this may be due to the similarity of pronunciation. It could also be considered to be a lexical error. However, it is not a grammatical error, but a semantic error, because the sentence structure is correct.
This may be referred to as a typo, a spelling mistake, a misspelling or a semantic error. These are not considered grammatical errors and are instead viewed as spelling mistakes. It is unclear whether there is a special term for this type of mistake but possible terms include "typo" and "semantic error".
Not a grammatical error, but a semantic error, because the sentence structure is correct. This could be seen as a spelling mistake and this may be due to the similarity of pronunciation. It could also be considered to be a lexical error. 
This are considered spelling mistakes. These are not grammatical errors since the sentences would be correct once the spelling mistake has been rectified. It is unclear whether there is a special name for these types of mistakes but possible terms include "typo" and "semantic error".