What do you mean, “tricked”? The method is original to me and I don’t think it has spread very far. Is there a Gregorian calendar year for which the GP algorithm gives the wrong result?

The two methods are exactly - exactly - the same. Just different ways of phrasing. Don't fool yourself.

It's algebraically equivalent, but it's not the same procedure. The insight in Bumbledraven's Algorithm is that by factoring out an unconditionally-performed mod-4 step, the problem can be reduced to two cases.

The standard method and mine give the same result, and I believe that mine is simpler to carry out in your head.

In what way do you believe that I am fooling myself?

Not so much as fooling yourself, but I agree with the OP your method isnt really 'original' in the sense that it's indeed exactly the same as the 'standard' one, just a tad different in how you explain the math. E.g. 'if not ending in 00 throw away...' is really just the same thing as 'except when divisable by 100'.

To add to your comment, being divisable by 400 is also the same thing as throwing away the 00 and checking the remaining is divisable by 4. One explanation is just a rephrasing of the other for the exact same method.