Not true. Watch the video, you can see the straps hanging loose from the F-18 pilot.
If pilots were so strapped in why did 109 pilots remove their armored headrests?
”Only the protective armor plate behind my head kept me from being killed by a 20mm. I used to inspect all of the aircraft, as some men would take this plate out. It reduced rearward visibility by about twenty percent, so they removed it.”
- Johannes Steinhoff, The German Aces Speak II
You’ll survive bumping your head on the canopy, you won’t survive eating bullets.