I'm not sure how else to explain this but I'll try.
in general a miscarriage is not a choice - not conscious, purposeful etc
a non medical reason abortion is a choice - conscious choice, purposeful, ASSISTED, done by someone ELSE.
you can't choose to have a miscarriage without a purposeful action
you can't stop a miscarriage without purposeful action or intervention
to equate these 2 topics by saying they are biological is just being pedantic, because humans are biological, using your logic murder is a biological response.
the topic "When is miscarriage not abortion." isn't worded well to begin with since the words can be used in many context and can be synonyms of each other which is why I have specified them the way I have.
worded another way, an abortion is not miscarriage when it's done by someone else or something else not of the body.
as you can see the terminology has changed
"The conscious distinction by doctors of ‘miscarriage’ from ‘abortion’ (‘induced’ and ‘spontaneous’) may be seen to have reflected certain legal, technical, professional and societal developments. The distinction in language may also be read as part of the process of assigning meaning to those women to whom the language was applied, a process by which women who experience miscarriage could be defined as distinct from women who experience an induced abortion."
"The importance of ensuring appropriate standards of care is underscored by the estimation that one in five pregnancies will miscarry, and most of these women will seek medical attention."
(I didn't know the number was that high)