It's not cooking 101, it's at least cooking 102 or 103. I know you didn't do it intentionally, but when newbies get into a new subject they are often turned off by comments like yours which boil down to "oh noo you can't do it that way, you simply must do
insert term of art or else
insert negative hyperbole" - it's precisely what's meant by "gatekeeping". If I told my girlfriend a million Italians were crying because she made lasagna wrong she'd probably slap me.
It also gets into the complaint about cultural specificity from the original comment. It might be Cooking 101 - for French cuisine. But to insist people learn to make the French mother sauces from scratch before eg. tacos or curry seems a bit too narrow-minded for "Cooking 101" generally speaking. I think "Salt Fat Acid Heat" has the right idea here.
edit PS: there is almost always a non-gatekeepy way to say the exact same thing. "In my experience, a homemade bechamel adds an incredible homemade taste to lasagna. I'd definitely recommend learning about the French 'mother sauces' sooner rather than later!"