It is. But because I’m a “belts and suspender” kind of person, plus I have this on my gravel bike, I used a velcro strap I had laying around in place of the rubber band.
Note: If you have a velcro strap that is long enough, you can fit it under the bottle cage so it works really well as a replacement for the rubber band as a secondary retaining option. Plus it won’t get easily lost out on the road / trail if you have to use the pump.
Edited to add the Note