Traditionally, platform engineering refers to a design optimized around creating and maintaining multiple versions of a product with different sets of features (and often different price points).

Note that platform engineering refers to the design priority, not the implementation.

For a dumb example, the implementation of free-profession-enterprise tiers for a web service might reflect platform engineering.

Or the implementation might be totally ad-hoc.

Or somewhere in between.

To explain further, feature flags are a technique that can facilitate platform engineering.

So platform engineering is a real and established thing.

But that doesn't preclude it being used as a buzzword by someone who doesn't know what it is.

Good luck.