The 1st video he just shows that XMRTraderAU used to have the username XmrAus2. The username change was requested by the seller months ago, and it can be seen in the trade chat in same video that in September he was already referred to as XMRTRaderAU.
Username changes on our platform is standard procedure, anyone can request it. Here's a couple of examples:
https://archive.ph/lxkuOhttps://archive.vn/ZLU3SThe second video demonstrates BuyCoinFast's account being banned, correct.