A pre-planning meeting is not part of the formal planning application process. It is not possible to definitively state that "pre planning" meetings are not regarded as a lobbying activity. It would depend on who attended the meeting and the matters discussed.
A pre-planning meeting where the only matters discussed concern the sharing of factual information would not be regarded as a lobbying activity. Similarly seeking or obtaining information or sharing information for the purposes of complying with a local authority’s policy or relevant planning legislation would not be regarded as lobbying.
On the other hand if a change to a local authority’s policy is being sought or discussed or an attempt is being made to influence a planning outcome during a pre-planning meeting it could be regarded as a "relevant communication" and a lobbying activity.
Ultimately it will be a matter for the person seeking the pre-planning meeting with the local authority to decide whether a "relevant communication" took place (i.e. was a "relevant matter" discussed with a DPO during the meeting).