Yeah, running TikTok on BlueStacks 5 and getting your account restricted is definitely a bummer. It’s highly likely that TikTok is flagging your account because it's noticing you're not on a mobile IP. Apps like TikTok use various methods to detect emulators like BlueStacks because they want to prevent spam and fraudulent activities. Using a mobile device or at least a VPN that offers mobile IPs might help you avoid these restrictions.
Yes it is because you are using bluestacks and TikTok can tell you're using an emulator instead of a normal phone.