All it takes is one lucky hit on jetliner.
Has to be a really lucky hit. They have something like maybe a 1 in 10 chance of actually hitting anything to start with and it turns out a modern jetliner is something the seeker head doesn’t see real well. Especially with the relatively cool exhaust of their high-bypass turbofans. In 2002, someone flipped 2 Strelas at a passing 757. Neither got close to the plane. There have been several other attempts on jetliners with the SA-7/Strela, and none have been successful in over a decade, including several reported mass firings.