I genuinely don’t understand how it can be the top podcast if it’s one and only episode is not Spotify’s top episode?
If I had to guess, I'd assume it works on some sort of average system, based on the last X number of days or something. The podcast series that are above it in the "top episodes" list presumably have other, less popular recent episodes that bring down any average score (however it's calculated), but Meghan only has one episode so far and it's pretty popular. Only having one episode to base it on will skew it a bit I guess, because from the top episode list it does look like Joe Rogan should be the top podcast overall.
The Daily, for example, is a daily (obviously) podcast from the New York Times - it has one podcast in the top episode list, but in the past few weeks will have released about 20 other episodes which obviously aren't as popular. I have no idea how often Joe Rogan releases podcasts or how many there are.
Or it might be that the charts cover different times. Eg the series chart might be most popular today, the episode chart might be most listened to this week. Her podcast has only been out a day or two, enough to be the most popular yesterday, but not long enough to be the most popular in the past week. This would be an odd way round for the charts to be set up imo, but it's possible.
Or it might be measuring different things. Is the episode chart based on how many people have listened, but the series chart based on subscribers for example.
I have no idea. But I don't think the difference means anything has been fudged or there's anything to be suspicious of.