Since the formula in A2 is =B1+10 and this formula was copied to A3, the formula in A3 is also =B2+10.
To solve this problem
Since A2's formula, =B1+10, was copied to A3, A3's formula, =B2+10, was likewise copied to A2. This is so that the relative references are changed to reflect the formula's new location when it is duplicated.
So, Because A3 is one row below A2, in this instance the B1 reference in the original formula is updated to B2.
Therefor, the formula in A3 is also =B2+10.