We took a look at FAA Order 7110.65, which is the "rule book" for air traffic controllers, to find out more. In 5-7-3(b) it says, "to aircraft operating beneath Class B airspace or in a VFR corridor designated through Class B airspace: assign a speed not more than 200 knots."

In 91.117(b), the speed restriction around Class C and D is prefaced with "unless otherwise authorized or required by ATC." This phrase is not used regarding speeds under the shelf of Class B airspace, nor is an exemption found in Order 7110.65.

Based on this, the answer is "no". You cannot fly faster than 200 knots under a Class B airspace shelf. Just like pilots, controllers make mistakes, and this controller likely forgot the regulation.