Most GMB insight discrepancies can be attributed to them just not being that accurate overall. So this type of observation is fairly common.
One possibility if it's not simply a matter of being inaccurate is that one of the sections is calculating direction requests to the actual business and the other one is calculating all direction requests to the address which would normally be higher if there are other points of interest at that address.
You've made me curious though so I am going to ask Google.
Definitely something is being recorded differently. The help page has a note about unique users. Maybe the Zip code map is not filtering unique users.
Note: This graph displays the number of unique users in each source location (i.e. postcode, city, and country). This means that a single user can request directions to a business 100 times in the aggregation period (7, 28, or 91 days), but we would only record one request.
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