Aren't a ton of Lemmy users from Reddit? That being said, I've had more positive interactions here than on Reddit, but I haven't been on Lemmy that long.
The subset of users that switched to Lemmy is smart enough to get over the "select an instance"-hurdle and fine with being on a smaller website with less content. This results in a different kind of interaction. Poeple here seem to still remember that there are actually living people behind those usernames. If Lemmy keeps growing there will be more chances to have the proper "go fuck yourself"-kind of interaction we are used to.
Since Lemmy isn't for profit I think that'll delay features that cater to the lowest common denominator, thus extending our current period of quality discussions.
To be honest i think it is just number and bell curve. A smaller user base will have less extreme, and strangely more opinions as no critical mass for a general trend to be form. Just my guess and source is trust me bro.