This is not a Chan_PJSIP related setting. It only applies to Chan_SIP which has the allowguest= option. PJSIP does not have this option because PJSIP doesn’t have a concept for anonymous. It just doesn’t accept any calls. It also doesn’t have global settings, i.e. a single setting that is applied to all the endpoints. Each endpoint must be configured for the options you want.
In order for PJSIP to accept anonymous calls, it needs to have an actual endpoint created called “anonymous” in order to do that “Allow Anonymous SIP Calls” must be set to Yes. So this has nothing to do with Allow SIP Guests (unless you have Chan_SIP peers) but the fact you are allowing anonymous calls to come into your server. Because of that, FreePBX created an anonymous endpoint to accept those calls.