In chapter 15, mayfeld asked what the creed said. Is it that he can’t show his face, or is it that he can’t take off his helmet? Because there's a difference.
In chapter 17, we get the answer. He’s not supposed to take off his helmet, and the oath says nothing about living beings or covering his face. So we know Din has been pushing it since chapter 8, when he let IG-11 remove his helmet, and in episode 15 he flat out broke it by wearing a different helmet.
So even before he found out from Bo-Katan that other Mandalorians think he’s a cultist, he was thinking about his creed and what it meant, and the reasons behind the rules. He hasn’t just been mindlessly following it. When Mayfled was asking him those hard questions, it wasn’t the first time Din had heard them. He’d been asking them himself for some time. Before chapter 8, he was thinking about why he can’t remove his helmet, and interpreted that it must be to hide his face from other living beings, and he reasoned that abiding by the intent of the rule (to hide his face) is equivalent to abiding by the rule (to never remove his helmet in the presence of another).
It’s difficult to determine the exact and true reasoning behind a rule, and if you decide to follow your interpretation of a rule instead of the exact wording, someone else is always going to say you’re breaking the rule. Some other dude in his tribe could say the reason is to make sure your head is always protected, or to make sure you always have access to the fancy tech inside the helmet. Both of those interpretations would allow for different loop holes than the ones Din exploits, but none of them actually exist within the wording of the oath.
Tbh, I really do believe Bo-Katan when she says his tribe is shitty. The rules they have are actually, physically harmful. Like in episode 8 we learn he can’t take off his helmet even though he is actively dying. He is expected to either die a Mandalorian or live as an apostate. That’s fucked up! And his tribe makes such a big deal about foundlings, but he can’t remove his helmet to save one without becoming an apostate. Upholding your duty to to foundlings is less important than wearing your helmet. Yikes!
Anyway, all of this is to say that he’s not a mindless zealot or a crazy cultist, and while his creed is a core part of his life and who he is, he’s been chafing under it for some time now. He’s realizing that the creed he swore to and has shaped his life around isn’t lining up with what he believes to be fair and just. Why should he be scorned and punished for saving someone, especially a child he is responsible for?
The armorer and the others of his tribe don't even ask him why he removed his helmet. They don't care. Apparently, no excuse could be good enough.