I don’t know if you read the right wiki, but in the history section the first paragraph is:

The Julian day number is based on the Julian Period proposed by Joseph Scaliger, a classical scholar, in 1583 (one year after the Gregorian calendar reform) as it is the product of three calendar cycles used with the Julian calendar:

28 (solar cycle) × 19 (lunar cycle) × 15 (indiction cycle) = 7980 years

Its epoch occurs when all three cycles (if they are continued backward far enough) were in their first year together. Years of the Julian Period are counted from this year, 4713 BC, as year 1, which was chosen to be before any historical record.[28]

It was either that, or earlier, or in the future. That’s the only year that kinda makes sense (solar = lunar = induction = 0). It looks odd but once you know you know, you know?