A misfire is a failure to combust the air/fuel charge in the combustion chamber during the expansion stroke, and they aren't typically caused by muffler deletes.

They can lead to the popping sound you're describing, but they don't always, and they're far from the only cause, and muffler deletes aren't necessary for those either. Unburned fuel hitting oxygen in the tip of a hot exhaust and immediately burning is the direct source of the noise, and causes for that are numerous.