I would not literally believe what he said. Obviously, he would have said this based upon what his engineers/scientists told him.
It could have been much more challenging than it is with current gravity. The factors that would come into play are as follows -
More fuel required to launch and then to slow down and land
Higher orbital speed, so harder re-entry
Thicker atmosphere, so more heat, and even harder re-entry.
More difficult design for the heavier take-off and higher escape velocity, you might need more/multiple thrusters.
Stronger material requirements to overcome the re-entry stress and heat.
Without going into calculations, it could be much harder, but not impossible. I am not even sure at what value of gravity, it would become impossible, if at all.
On the other hand, we could have possibly had stronger materials available due to stronger gravity.
What he may have meant is that it may not have been economically viable to do so. But we do not know what kind of economy we would have with 10% stronger gravity.