I don't think so. I mean, it's possible, but I doubt it. Ethel clearly calls the magic Netherese/ Sharran Shadow Weave Magic. That's different from anti magic. Now, that said, I agree there may be a connection, and perhaps it all started in 1481 with the meeting of Mystra Clerics.
I also think Gale is more involved and knows more than he's letting on. Why didn't he connect when you first meet him? Perhaps he knows more about how to control the tadpoles since he knows Netherese magic... Aka the Fast Travel Netherese Portal Runes.
