I think you’re underestimating his speed and overestimating the strength of airframes. Most planes can easily get to speeds where inputs can exceed structural limits under normal flight conditions. There is even a V speed for it, Va or maneuvering speed. A quick google suggests that Vne, or “never exceed” for the PA 25 is -35 knots and Va is 104 knots. Now I have never flown one and I haven’t completely verified them but they sound about right. At 104 knots he can over G the airframe. Assuming a standard safety factor of 1.5 and a g limit of 3.8 (basic assumptions but I can’t find actual data for the PA25) and at max weight you can expect severe structural damage with full control inputs at 127 knots. If he wasn’t carrying that much and was lighter that number comes down as well. Finally, there’s the fact that it was a crop duster in Mexico so who knows what the maintenance history and actual condition of that wing spar was. Either way, even if it was in top form hitting 130 knots on a show boating low pass isn’t that crazy.