It's a pity that they named it like that. "Instance of" implies the primacy of classes. In OO you need a class as a template to create objects, in RDBMS, you need a table to store the data. KGs, esp those using RDF, bring more possibilities mainly because they don't require a pre-defined schema. Linking to a class can be (a) postponed, (b) new classes can be created after the entity was created, and (c) classification can be inferred (which, by the way, is daily performed by people querying WD with the property path `wdt:P31/wdt:P279*`).

Luckily, WD uses opaque URI, so one day they may decide to change the label to "is a" or "type" or "is of type".