The key for me here is you "didn't have a clue" until looking it up. So clearly your area isn't absolutely overrun with little Noahs, otherwise you would have worked it out a lot sooner.
Popularity varies from area to area. Some of the top names around me seem to be Arlo, Caleb, Harper, Luna, Mila, Aria... none of which are in the national top 5. Some of the national top 5 names are popular around me (Oliver, Noah, Olivia, Isla) but hardly an Ava, Amelia or George to be seen).
Point is, it really doesn't matter what is popular across the country as a whole. It doesn't necessarily mean it will be popular near you. Even if it is, who cares? Days of 3 in a class are all but gone as people choose from such a larger pool of names now than ever before. If it does happen, it's just a coincidence and can happen to any name. Imagine picking something you love much less and there being another in his class at school, and no Noahs. It could easily happen. How would you feel?
It's much more important to go for something you love. There really isn't much difference between names in the top 10 and names in the top 20 in terms of usage. There isn't much difference between the top 20 and the top 50, top 50 and top 100 etc. I could go on. Why limit yourself to silly rules that you won't pick it if it falls in a certain position nationally?
You love Noah for a reason, and until you read that list you were oblivious that it was currently the most popular name in England and Wales. That proves to me that it really can't matter that much.