That's specific to HSA to HSA, traditional IRA to traditional IRA and Roth IRA to Roth IRA (tracing back to IRS Revenue Ruling 78-406 which defines a trustee-to-trustee transfer, a rule established to allow movement of these types of accounts from one custodian to another without regard to the one-rollover-per-12-months limitation by it being neither a distribution nor a rollover). Movement of funds to or from a 401(k) is always reportable (except for the case where one company acquires another resulting in the merger of two 401(k) plans).
