Do you use the "old" reddit view? Reddit introduced display names separate from account usernames, but old reddit doesn't show them. The user that shows up as Incendiary-Leg-8592 on old Reddit might have simply accepted reddit's suggestion when they created their account, and appear to everyone else (whatever the old/new reddit breakdown is) as something less spammy looking.

Assuming you do indeed still use "old" reddit, the next time you see such a comment, open their account page in a private window (or any browser that isn't logged in). They might look different to themselves and most others.