First, test results are only as good as the people doing the tests
Second, they are only as good as the test kit used.
I cannot comment on either your or the pool stores testing methods but I do know this. The CH on the walmart Aquachem kit does have some problems. The indicator turning yellow has been documented by myself and others in a different thread. Sometimes this test works fine and sometimes it doesn't. I suspect that high chlorine levels are causing the interferance.

The copper and iron results you got mean that the sequsterant you added had worked and made the metals in your water non reactive or that the testing procedure is not correct.

If the pool store is using LaMotte testing (small plastic vials of powdered reagent injected with pool water) then I can explain the low TA readings. The TA test needs to develop for 1.5 minutes and needs to be read before 5 minutes has elapsed. If not it will read low. (It will also read low if the chlorine levels are above about 6 ppm but it doesn't seem to really affect the test until the chlorine gets to about 9-10 ppm) Ditto for the CYA test except it needs to develp for about 2 minutes as does the copper test. The iron test is supposed to develop for 3 minutes before reading. Also the LaMotte test is a total hardness (calcium and magnesium hardness) test and not a calcium hardness test.

If they are using a different test chemistry then I really don't know except that some pool store water testers really don't do a very good job with their testing.