I think it's a bit of weird language. From comparing what specs I could find Energia had significantly greater LEO capacity (200% of Falcon Heavy), and a slight advantage in GTO payloads, a slight disadvantage at trans-lunar payloads and has no capacity at all for trans-Martian payloads where the Falcon Heavy can deliver 14,000kg/14 tonnes/30864.717lbs of payload.

So I think they are claiming that title due to Energia dropping off after trans-lunar ranges assuming Falcon Heavy reaches "orbit" and then travels further beyond.