I'm guessing that pic was taken with the suspension hanging & the wheel off?? :dontknow:
If so, then it's very likely that your airbag had minimal pressure in it when you turned the ignition off, then you lifted the rear & removed the wheel..... So now that the suspension is hanging and your airbag hasn't been pumped up any more by the ACS plus all the inflate/deflate &/or non-return valves are firmly closed, it's simply been stretched out beyond the ability of what little air remains inside it to inflate it, and what you see is
EXACTLY what your airbag should look like! :thumbup:
I wouldn't worry too much unless it looks like that once the wheel is re-fitted and back on the ground - if it looks like that then, you've got problems! But as it stands, looking like that with the rear suspension hanging to full extension, it's just proving that your airbag & the associated valves have NO LEAKS, which is a GOOD thing!

hyea: