Python 3, 51 44 43 41 bytes
-7 thanks to loopy walt's suggestion to use *open.
-1 thanks to xnor's suggestion to replace any(...) with 1in ...
-2 thanks to dingledooper's suggestion of using str.find instead of str.__eq__
0in map(str.find,*open(0))or print('yep')
This is a full program that takes input from STD INstdin until an EOF (which we assume the user provides at the end of the second line) with open(0) and maps across the two strings by splatting (*), calling str.find on each pair of characters in turn. If 0 is in the result (i.e. the characters are equal and so the index of the first in the second is 0 rather than -1 for "not found") then the right-hand clause of the or is not evaluated, and so we don't print.
My previous version, with xnor's and dingledooper's suggestions, at \$48\$, is interactive without the EOF faff:
0in map(str.find,input(),input())or print('yep')
You could save one more byte by printing to STD ERRstderr instead of STD OUTstdout by exiting the program early using exit in place of print.
A note to your son - this is not how I'd want someone in my team at work to write code :) - readability counts, a lot.