From my knowledge and review of ISO 22000, there is no direct requirements that states the internal audit has to be completed by a GFSI experienced auditor. All the standard states under 8.4.1 Internal Audit is that selected auditors are to be objective and impartial and they shall not audit their own work.
From a training perspective, under 6.2.2, the auditor would need to be trained and competent in the role that they are undertaking. one of the key skills of internal auditing is knowing the rules by having a very good understanding of the standard (audit criteria) and being able to determine compliance against those requirements.
Like anything with auditing, if an auditor makes a suggestion or non-conformance that you are not sure about - always ask "can you please show me where in the standard (that you are being audited against) that xxxx is a requirement". This helps to avoid auditors making unsupported requests of a business.
I hope this helps