He may well have, and it is probably true but what other planes did he fly he was at the time just a good trainee pilot. He trained on P39s and then went operational in UK in the P51. To me all he is saying is that he preferred the P39 to his basic trainers, well almost all pilots do.
From Wiki
Soon after entering service, pilots began to report that "during flights of the P-39 in certain maneuvers, it tumbled end over end." Most of these events happened after the aircraft was stalled in a nose high attitude with considerable power applied. Concerned, Bell initiated a test program. Bell pilots made 86 separate efforts to reproduce the reported tumbling characteristics. In no case were they able to tumble the aircraft. In his autobiography veteran test and airshow pilot
R.A. "Bob" Hoover provides an account of tumbling a P-39. He goes on to say that in hindsight, he was actually performing a
Lomcovak, a now-common airshow maneuver, which he was also able to do in a
Curtiss P-40.
[36] [N 6] An informal study of the P-39's spinning characteristics was conducted in the
NASA Langley Research Center 20-foot Free-Spinning Tunnel during the 1970s. A study of old reports showed that during earlier spin testing in the facility, the aircraft had never tumbled. However, it was noted that all testing had been done with a simulated full ammunition load, which drew the aircraft's center of gravity forward. After finding the original spin test model of the P-39 in storage, the new study first replicated the earlier testing, with consistent results. Then, the model was re-ballasted to simulate a condition of no ammunition load, which moved the aircraft's center of gravity aft. Under these conditions, the model was found to often tumble when thrown into the tunnel.
[38]