I know one of things someone pointed somewhere is Gale's knowledge of Netherese magic. Not to say he is well verse in that type of magic but in a conversation that I saw he kinda gives you the impression that he knows more than he's letting on. We know from Auntie Ethel that the tadpoles have been tampered with Netherese magic. Did Gale sense Netherese magic in his tadpole but didn't say anything to us? Which could be why he seems more in control of his tadpole and even able to block us out as you said. It's one of the reasons why I have mixed feeling about Gale. There seems to be something off about him. Nothing necessarily bad just off.
It's true that we know he's studied Netherese magic quite extensively - that's an important part of his own situation, after all, and he makes no secret of that. I find it unlikely that he'd be aware that the tadpoles were tampered with using nethersese magic since he's a Wizard - he can't innately sense for feel the weave at all, and performs most of his magic through raw intellect and precise form; to make an analogy - he knows just precisely how to put the pipes in place and how to make the water flow, to make a beautiful fountain appear, and he knows it well enough to do it with a blindfold on, but he cannot actually feel the water flowing, as a sorcerer can. At best he feels the vibrations that the pipes make when it does flow, but not the water itself. Gale has to evoke a specifically designed spell in order to let him actually feel the weave - that's what he's doing in the weave scene - any other time, he doesn't actually feel it. It's why your sorcerer has a line in response to say that that's just what you feel every day, and Gale is wistful when he hopes that you appreciate what a gift that is.
So, unless he turned very specific magic on the tadpole in his own head, he's not going to feel anything from it. The one gap there is that, being the person he is, I'm sure he'd absolutely have tried to do everything he could to study and examine his tadpole situation, which would likely include trying to detect if any magic was present in it, as an answer to why they hadn't started turning... but we don't have those spells in the game, either... so... I don't know what the answer is there.
