Summary
The visual editor for merchandising rules uses the product ID to register the rules, but they are processed on top of a more generic field, which includes more than just the ProductID but also the ProductRefID, SKUID, SKURefID, and EAN, as per our documentation.
If the value from a product ID is also part of a different ID field in another product, the rule will be applied to both of them.
The same issue also happens for merchandising rules created with the manual editor while creating rules by the ID attribute if the value exists in more than one product, but in this case, it's possible to workaround using different ID values such as SKURefID or EAN, which are more likely to be unique.
Simulation
Consider product A with "productId=444" and product B with "productId=555", where the SKU from product A is "skuId=555".
A rule to pin or hide product B (productId=555) will also be applied to product A (due to skuId=555).
Workaround
N/A