If he used online calculator , its accurate.
The validity of the online calculator depends on the accuracy of ALL dates of travel entered. Many, many applicants make mistakes in entering the data. Some of the commonly made mistakes only affect the calculation by a day or three, like applicants who rely on passport entry stamps, into another country, for dates of exit from Canada (which are often off by a day or two). More than a few fail to account for each and every trip, so fail to account for days or weeks abroad. For those who make mistakes, an overriding issue is whether they applied with enough of a buffer to cover the error.
So, no, just because an applicant used the online calculator that does not mean the calculation is accurate. It is only as accurate as the data entered. We all make mistakes (those who are sure they did not make any mistakes are almost always mistaken about that). This is why the conventional wisdom urges prospective applicants to WAIT to apply until they have a comfortable margin, a "buffer," over the minimum presence requirement. To accommodate oversights and other errors.