Atheists don't claim to know the truth, we don't claim to know anything.
Most atheists presume that if God exists there would be evidence of it, and they would be able to recognize this evidence and judge it to be valid and convincing. They are so certain of this presumption that they are constantly proclaiming that they are seeing no evidence for the existence of God, and therefor it is logical that they assume no gods exist.
We just find that the God claim does not yet have sufficient evidence to be convincing.
Yes, because you are blindly and illogically assuming that if such evidence exists, you would know of it, and be able to judge it's validity.
Convincing you, then, is in fact the criteria that you are holding onto for establishing the existence of God/gods. If
you are not convinced, then it must be assumed that no gods exist.
Every atheist knows in his heart that this is completely illogical, which is why they try very hard not to actually say it out loud in this way. Yet they do say it all the time in one way or another. And they do assume that all theists are fools playing at make-believe regarding the existence of any gods because they "have no evidence".
Good luck, however, getting a single one of them to admit to any of this. Or to even seriously consider it. Because all that open-mindedness and free-thinking vanishes the instant they get called out in the way they are constantly calling out everyone else.
This discomfits theists for some reason. Perhaps they realize, deep down, that their claims don't stand up to scrutiny, and feel threatened by anyone pointing this out.
I think most theists understand that theism is about faith, not evidence and not blind, egotistical proclamations of belief. But some theists don't understand this, and those are the theists that the atheists constantly refer to and present as being "theists". Just as you have done, here. Because they are the ones you can most easily throw stones at.