Well spotted! That’ll be the ‘initial datapoint’, so special for other reasons.
Looking behind the scenes, this is a binary goal in terms of how it aggregates.
That means (to my surprise, I admit) that it checks for the presence or absence of a datapoint. If you enter something (or several things), even if it’s a zero, the day’s total aggregates as ‘1’.
Those two lighter bold dots are days on which the aggregated value, ‘1’, differs from the entered value, ‘0’.