Blame the skill and his ability to choose the correct materials and methods. The Tapcon should NEVER be installed in the mortar joint, and the washer needs to match the diameter of the screw.
Tapcons are made of tough high carbon heat treated steel, that is at least 85,000 to 100,000 PSI tensile strength or more Ever try to snap off one of these tough cookies?
I HAVE snapped tapcons off, that said, I like them and use them in concrete and or mortor joints daily.
Who ever told you not to use them in mortor joints, IF you use the correct size for the project you should not have trouble with them at all.
Jimbo