I am not sure if they have that dogmatic belief. I have never seen an atheist that claims that all Muslims have the same beliefs. But to be fair Islam appears to have a higher percentage of literalists than Christianity does right now. Applying those beliefs even to the hadith. I know there are many that do not do so. But there are countless Muslims that will defend the actions claimed of Muhammed in the hadith that you mentioned in your OP.
I am not sure if they have that dogmatic belief. I have never seen an atheist that claims that all Muslims have the same beliefs. But to be fair Islam appears to have a higher percentage of literalists than Christianity does right now. Applying those beliefs even to the hadith. I know there are many that do not do so. But there are countless Muslims that will defend the actions claimed of Muhammed in the hadith that you mentioned in your OP.
I am an Islamic Qur'an Literalist, I believe that the Qur'an may use symbolic language, but is mainly Literal and meant to be taken as Literal and talking about Literal things Literally, bringing up interactions meant to be understood as having actually happened, discussing scenarios that are meant to be believed as real, and even insisting upon the reality of such "is this then magic?" making it clear that the people who think this is magic or falsehood or trickery are the ones who will be in error.
The people who believe in the Hadith (I'm not one), also believe it is literally true, true accounts of things said and done, and it appears that it was meant to be understood as that also by those who collected such saying or in my belief may have fabricated some or all of them or received them from ultimate fabricators, but all were meant to be "true stories" as far as I think it was supposed to be understood.
There are also non-Muslims who consider these stories to be either based in truth, partially true, or entirely true (likely except the miracles maybe, or even the miracles possibly being really witnessed or experienced but there being some other explanation possibly than the one a believer might choose).
Similarly, there are non-believers in the stories of Jesus found in the Gospels who believe in them as true, or based on truth, and all the same.
There are also those who don't believe in them, but want to insist that "you have to believe in them if you're part of this group" in order that "you can thus be proven to be bad or stupid" by following such literally, or even symbolically.
These are the types of people:
A person who wants to convince you to leave whatever beliefs or practices you do or associate with and abandon it all (not caring necessarily what you replace it with).
A person who wants you to be like whatever they are (or something else specifically, even if they aren't themselves that).
A person who doesn't care much at all.
A lot of people think or wish they were the apathetic third type, but many people are not, however much they may wish to be, and instead it is the human nature apparently to want others to be like ourselves or at least not what we think is bad in some way. We thrive on enemies, but also want to make friends out of people, and remove the blockages we may perceive as in the way towards our being friends or "same-same".
I want everyone to think and believe as I do, so that I can like them more, because then what they say and think meshes with my worldview better and what I say and think, I even want them to have similar tastes as me so they can give me useful and good food recommendations and I can expand "myself" through them, like one big "Me" across the world.
Yet, seeing that people are highly resistant to becoming my thorough little buddies, I have increasingly felt irritated with them, leading to that third option "not caring much", but that isn't so, its more like wanting chocolate, seeing chocolate right before you, but its fake or you can't have it, or its just a mirage and you'll never be able to have it, and so instead of not actually caring, I just feel annoyed and agitated by all the potential people I perceive as never respecting me or being respected by me very much, since we both secretly must think we are each stupid for not believing the same things.