Mdd, the qualifier isn’t being an apikores; if someone is not aware of a commandment, or a Commander, or that the Commander gave that commandment, then he’s not doing anything.
The average frei person never heard of tefillin, and definitely doesn’t think that Hashem commanded him to do so.
Maybe this would apply to some sefardim, but chabad just asks people if they’re Jewish and plops it on them, in full view of pritzus sometimes, which is shelo k’din.