People for decades have been convinced that there's one "right" way to make Yorkshire Puddings. The reality is that most if not all of these "tricks" are either unnecessary or outright hurt the outcome.
Kenji over at Serious Eats went a bit bonkers and tried out just about all of the different methods and has summarized it in an article which is paired with his "best Yorkshire puddings" recipe.
While testing the order of adding milk and eggs to flour actually wasn't one of the things he does, the first step of his recipe is to simply mix together the flour, eggs, and milk (plus a tablespoon of water and some salt) - all simultaneously.
- Combine eggs, flour, milk, water, and salt in a medium bowl and whisk until a smooth batter is formed. Let batter rest at room temperature for at least 30 minutes. Alternatively, for best results, transfer to an airtight container and refrigerate batter overnight or for up to 3 days. Remove from refrigerator while you preheat the oven.
If you're really interested in Yorkies, I strongly suggest you read his article and consider trying the recipe out for yourself. If you want a summary, I've created a shorter version of it in an answer on this previous question.