Did the pond go all of the way dry after completion, but now it has 2.5' feet of water?
That sounds a little bit more encouraging! (But is not yet proof of sealing.)
I did Pond Geology 101 above. If you want to keep reading, I will go to the 201 class.
Some groundwater tables are very well tied to the surface soils and/or rock outcrops, and can rise or fall on relatively rapid time scales. My farm has very sand soil and the aquifer has many connections to the surface of the land, including a creek in my tiny valley. I have seen the water level go up in my ponds after it did NOT rain at the farm. However, there were heavy thunderstorms in the drainage basin of the creek. As the creek level rose, the local water table went up, and my ponds also went up due to the unsealed aquifer allowing more water into the ponds.
Some groundwater tables have fewer connections to the surface, and their fluctuations are generally measured over the period of years or decades. Those are more stable and you would see your pond go down during a multi-year drought or go up after several years of above average rainfall.
Finally, some groundwater tables are so stable that they are said to contain "fossil water". Generally, that is water in a basin where the rivers and lakes are perched above the water table and there are very few connections at all to the surface. That water usually stays in place until humans begin to remove it via deep water wells. (You might have that kind of water table on your property in central Oklahoma in your sedimentary rocks, but that is NOT the type of water table that they encountered excavating your pond.)
I only typed all of that to help you as an observer of your pond. If you have heavy rains on your property, your pond should start going up due to the surface water collecting in your pond. However, it could also be going up by the heavy rains causing the groundwater table to go up. Or even a combination of the two mechanisms.
It will probably be easier for you to determine which, by observing how the water level in your pond goes DOWN. If it goes down substantially after just a few days, then you are probably still connected to the local aquifer. If it goes down slowly over several weeks without rain, then all of your losses could be due to evaporation and you have a properly sealed pond. (If you really want to do this, then read how to set up an evaporation pan test. The water level in the pan should evaporate a little more rapidly than the water level in the pond. If your pond is dropping faster than the pan, then you have a leak or are tied to the aquifer.)
Complications: New ponds must saturate all of the pore spaces in the sub-soil material PLUS the water that is incorporated into the structures of the swelling clays. If your pond has not yet done that, then you could have a sealed pond, but the water level dropped subsequent to the rise after a rain due to that process.
Also, if your pond was "sealed" with clay, but it was poorly compacted, then it might hold water as tight as a bathtub when it is only 1/2 full. However, when it fills all of the way after a big rain, it could then leak back down to the 1/2 full level due to the increased hydrostatic pressure of the full water column.
Hopefully, that covers a lot of your "it depends" scenarios!
How much water shed drains into your new pond? What is the plant cover and what is the slope?
There is a chance some good rains can turn your hole into a pond. Unfortunately, you may need to join the many other members on Pond Boss that perform rain dances frequently for their ponds.