Back to the original question. is it mashing if you are in your lowest gear? No.
and does cadence have anything do with mashing again? No.

Only time I would consider "mashing" is if you are only pushing down the pedals, forgetting to push forward at the top, sweeping your foot backward at the bottom and pulling up on the back side, then ITS mashing.

Your cadence could drop to 30 but if you are putting energy into the pedal most of the way around then its not mashing.

On a steep hill, I will stand up and allow my body weight to push the pedal down; but, I do use my other leg to pull up on the pedal. I skip the pushing and sweeping when I stand up so my muscles can take a short 10-20 second break. sometimes bit longer. And sometimes I do add the pushing part. My lowest gear combo is ony 39/26?? on the road bike (tt is 39/21 or 23) so when the hill gets to be 12% or more I have to stand.

Standing does use up more of your energy but sometimes its necessary to recover your regular pedalling muscles. or if the hills are too steep for your gearing.

not to fear, you are pedalling just fine.
Smilingcat