You're right, they are. If your data can't survive a single storage host vanishing from existence, you don't have a backup. If your data can't survive one predictable or regularly occurring catastrophic act of nature, you don't have a backup. If your data can't survive a piece of malware -- with all of the credentials you have -- erasing it, you don't have a backup.
EDIT: Also, if you don't regularly test that your backups actually work, you probably don't have a backup. Lots of companies learn that one the hard way.
Yes, they are as guilty! You say that as if it's a ridiculous assertion. Have you not read the occasional HN submission where someone is locked out of their cloud provider for dubious reasons?
But where are you seeing this vendor was tasked with backups? This looks like a single copy situation.