Really fast attenuation with starter. Is this to be expected

A little bit of background: I finished brewing a black IPA and pitched yeast around 5:00 on Sunday. Admittedly, the wort was a little warm (75F), because it was 9 degrees outside and I was in a hurry to get back inside. The yeast was made from Wyyeast #1056. I made a starter on Thursday, after the major activity had subsided, I put it in the refrigerator overnight, decanted the wort and added more boiled wort. On brew day I decanted again and gave the yeast about 3 hours at room temperature before pitching. BrewSmith estimated 378 Billion cells prior to the decant. I'm not sure how to account for that in the software.

I realized today (Monday morning), that I forgot to get the OG. Considering it had only been 14 hours I figured the yeast would still be in the growth or lag phase. Even when I have really active ale yeast, it still usually takes 24 hours to get through the lag phase. My plan was to take readings with both my hygrometer and refractometer, so I could back calculate the difference and estimate the OG.

Approaching the fermentation bucket, it didn't look like the airlock had seen any activity but I could smell what in my opinion was healthy yeast growth. The lid was a screw on lid and the gasket seal broke last time, so it may have vented through there. I removed the lid, looked like pretty typical growth, when I checked the gravity, it was fully attenuated. Is this normal in 14 hours? Given the temperature and started probably helped but I have never seen attenuation occur remotely this fast.

Edit: 5 days later:

Normally I wait at least 6 days before moving to secondary, but whatever happened, this was done days ago.

As suggested I used the OG estimator in Beersmith. I figured doing this was possible, but wasn't sure it would be all that accurate with only two data points.

fg (Hydgrometer/refractometer) 1.008/1.022

Beersmith estimated the OG at 1.087 based on the calculation

The recipe estimation was an OG of 1.083 and an FG of 1.021.

Well, I guess may major concern about low attenuation isn't a problem. I don't entirely trust the back calculation but the extra steps in the started prep seemed to pay off.