Confirmed. ;) The reason it is showing this way is the population is capped to what it is currently plus tokens (likely).
Any additional added population would need 4 x (four times) county parcels to support it.
In order to add your +125 the county would need to have 932 parcels total in the county, e.g. 108 + 125 = 233; the desired population requires 233 x 4 parcels.
It's an exceedingly small county with just 238 parcels =P
It does show additional pops for tokens though - likely regardless of the number a Count may have.
(( very sweet county location btw ))
Which if I think about lol; the cap was only intended to cap the parcels for the settlement, but seems to be capping pop too. Needs a confirm or look. Cheers!