It does present a bottleneck, but not significant relative to the other larger pipe. He likely had to reduce to 3/4" on both ends to match the fittings. The reduction at the end (heater) is completely fine. The one near the meter, might present a problem (pressure droop) but that would only be under heavy load/usage. Think of it like a garden hose - if you put your thumb on the end you can feel the pressure build until you let it go and then pressure drops and flow levels off. Now kink the hose 50' from the end and you'll lose both flow and pressure (pressure droop) at the end. Gas flow is similar, not identical but similar.
If you heater has an issue running I would look at removing the 3/4" reduction at the meter if possible. The one near the heater would be unlikely to make any difference unless your heater valve has an 1.5" inlet. Most gas valves are 3/4 inch.