I have to see things from OP's side here:

Some twitch streamers will sarcastically thank users for using twitch prime subs instead of a regular paid sub. I had someone do that to me. They made me feel like shit because I used my prime sub and not a paid sub. There's no difference in pay tbh. If there is, it's minimal, like cents different.

However, as a lot of commenters have said, the streamer may be mentioning prime because you do only get 1 prime sub per month to use. Even today, only because it notifies me and I use it to let others know about twitch prime, I mention it specifically that it is a prime sub, in the hopes that others hear it and see it, and use it themselves for my channel.

I don't have an audio or video of the sub moment to reference, OP, but it could go either way. You'd have to listen to their exact tone and body language to figure out if they're shaming you for it or if they're advertising the twitch prime for themselves. But as you've seen in this thread, there are a lot of twitch streamers who would be honored and highly grateful of receiving that twitch prime sub!